Glossary
C
184 terms.
- CAA record
A record that lists which certificate authorities may issue certificates for a name, and under what conditions. CAs check it before issuing.
Like I'm five A note on a name saying which certificate offices are allowed to vouch for it.
- Cache
A storage location that holds copies of data (such as web content) so that future requests for that data can be served more quickly.
Like I'm five A place where copies of popular content are stored for quick access.
- Cache key
The value a cache uses to decide whether a stored response matches a new request. The key parameter of Cache-Status can carry a representation of it.
Like I'm five The label on a stored item that lets the cache find it again.
- Cache-Control
The HTTP/1.1 header that carries caching directives such as no-cache, no-store, max-age, public and private, telling caches whether and for how long they may reuse a response.
Like I'm five A sticky note on an answer saying how long you may keep your copy.
Used in RFC 1152 RFC 1856 RFC 1862 RFC 2068 RFC 2187 RFC 2227 RFC 2295 RFC 2616 RFC 2703 RFC 3040 RFC 3229 RFC 3466 RFC 5222 RFC 5861 RFC 6707 RFC 7231 RFC 7232 RFC 7234 RFC 7337 RFC 7933 RFC 7945 RFC 7975 RFC 8007 RFC 8182 and 13 more
- CalDAV
Calendaring Extensions to WebDAV; an HTTP-based protocol for storing, accessing, and managing calendar data on remote servers.
Like I'm five A way to keep your calendar on a server and edit it from anywhere using HTTP.
- Call Agent
A controller that manages one or more media gateways, sending them commands to set up, modify, and tear down calls.
Like I'm five A computer that tells the gateway what to do with each call.
- Call home
A setup where the managed device opens the TCP connection to its management system instead of waiting to be contacted. The usual client and server roles above TCP stay the same.
Like I'm five The device phones the manager first instead of waiting for a call.
- Call Placement Service
A service in STIR out-of-band conveyance that stores PASSporTs so that the party receiving a call can retrieve them. It is also called a CPS.
Like I'm five A drop-off box where the proof of who is calling is left for the receiver to pick up.
- Caller ID spoofing
Making a call appear to come from a telephone number the caller is not entitled to use. It is used for impersonating a person or for hiding who is really calling.
Like I'm five Writing someone else's phone number on the caller screen so the person who picks up is fooled.
- Callout server
A remote server that an OPES processor can hand work to, either to spread the workload or to use a specialized service such as virus scanning.
Like I'm five A bigger helper that gets the hard jobs passed to it.
- Candidate pair
A local candidate matched with a remote candidate. ICE sorts the pairs by priority and runs a connectivity check on each one in turn.
Like I'm five One of your doors matched up with one of your friend's doors.
- Candidate path
One possible way to meet a policy, with its own constraints and goals. A policy can have several, and one is chosen as the active one.
Like I'm five One of several possible routes you could pick for a trip.
- Canonical form
The single agreed-on byte layout of a record or name ordering that signers and validators use so identical data always produces identical signatures.
Like I'm five Writing everything the same neat way before sealing it.
Used in RFC 886 RFC 989 RFC 1630 RFC 2015 RFC 2049 RFC 2065 RFC 2469 RFC 2470 RFC 3030 RFC 3076 RFC 3275 RFC 3597 RFC 3641 RFC 3862 RFC 4034 RFC 5952 RFC 7468 RFC 7638 RFC 7998 RFC 8785 RFC 8949 RFC 8976 RFC 9679
- Canonicalization
Turning a message into a standard form before it is hashed, so small harmless changes in transit do not change the result. DKIM defines
simpleandrelaxedforms for the headers and body separately. The message that is actually sent is never changed.Like I'm five Smoothing out a letter in your head, so a crease or extra spacing does not matter when you compare it.
Used in RFC 1421 RFC 1848 RFC 2276 RFC 2311 RFC 2802 RFC 2807 RFC 3075 RFC 3076 RFC 3156 RFC 3275 RFC 3741 RFC 3930 RFC 4130 RFC 4646 RFC 4647 RFC 4826 RFC 4871 RFC 5105 RFC 5485 RFC 5646 RFC 5751 RFC 5854 RFC 6008 RFC 6283 and 20 more
- Captive portal
A login or terms page that a public network shows before it grants internet access. RFC 6585 defines 511 for such networks to use.
Like I'm five The sign-in page you meet on hotel Wi-Fi.
Used in RFC 4058 RFC 6585 RFC 7050 RFC 8801 RFC 8908 RFC 8910 RFC 8952 RFC 9965
- Care-of Address
In Mobile IPv6, the address a mobile node uses on its current network, distinct from its home address.
Like I'm five The temporary address your phone gets when it connects to a new network.
Used in RFC 2002 RFC 2290 RFC 2344 RFC 2794 RFC 3024 RFC 3220 RFC 3344 RFC 3583 RFC 3753 RFC 3775 RFC 3776 RFC 3963 RFC 4068 RFC 4177 RFC 4225 RFC 4295 RFC 4433 RFC 4487 RFC 4636 RFC 4651 RFC 4857 RFC 4866 RFC 4886 RFC 5177 and 18 more
- Carrier Grade NAT
A NAT run in the provider's network that gives customers no way to control the translation or bypass it. It is also called a CGN.
Like I'm five A big sorting room run by the post office, where you cannot change the rules.
Used in RFC 6127 RFC 6264 RFC 6269 RFC 6333 RFC 6346 RFC 6598 RFC 6887 RFC 6888 RFC 7021 RFC 7289 RFC 7398 RFC 7422 RFC 7753 RFC 8045 RFC 8512 RFC 9313 RFC 9386
- Carrier-of-Record
The phone company that has authority over a block of phone numbers and controls what those numbers resolve to in ENUM.
Like I'm five The company in charge of a group of phone numbers.
- Case folding
Mapping upper and lower case letters to one common form so that comparisons ignore case. Which direction is used matters for consistent results.
Like I'm five Turning big and small letters into the same kind so they match.
- CBC mode
Cipher Block Chaining, a way of using a block cipher in which each plaintext block is XOR'd with the previous ciphertext block before it is encrypted. The first block uses an initialization vector.
Like I'm five Each scrambled piece is mixed with the one before it, so repeats do not look the same.
- CBC-MAC
A message authentication code built from a block cipher in cipher block chaining mode. Each block is XORed with the previous output and then encrypted, and the final output, possibly truncated, is the tag.
Like I'm five A fingerprint made by scrambling a message one block at a time, each block mixed with the last.
- CBOR
Concise Binary Object Representation, a compact binary data format. EDHOC messages are made of CBOR data items.
Like I'm five A way to write down information using as few bytes as possible.
Used in RFC 8392 RFC 8428 RFC 8610 RFC 8618 RFC 8742 RFC 8746 RFC 8769 RFC 8949 RFC 8990 RFC 9031 RFC 9052 RFC 9053 RFC 9090 RFC 9132 RFC 9171 RFC 9200 RFC 9237 RFC 9244 RFC 9254 RFC 9290 RFC 9338 RFC 9360 RFC 9393 RFC 9528 and 12 more
- CBOR tag
A number placed in front of a CBOR data item to say what kind of thing it is, such as a date. Tags are registered with IANA.
Like I'm five A sticky label on a value that says what it means.
- CBOR Web Token
A compact token format that carries claims, such as who it is for and when it expires, encoded in CBOR instead of JSON. It suits constrained devices.
Like I'm five A small digital pass written in a short code so tiny gadgets can read it.
- CD bit
Checking Disabled. A DNS header bit set by a resolver in a query to say it will do its own validation, so the recursive server should not withhold data that failed its checks. Servers copy it into the response.
Like I'm five A note saying "don't check it for me, I'll check it myself."
- CDDL
The Concise Data Definition Language, a notation for describing the structure of CBOR and JSON data.
Like I'm five A short way to write down what shape a piece of data must have.
Used in RFC 8610 RFC 8618 RFC 8746 RFC 9165 RFC 9237 RFC 9393 RFC 9682 RFC 9741 RFC 9999 RFC 10013
- CDNI
Content Delivery Network Interconnection, a set of interfaces that lets separate content delivery networks cooperate. An upstream CDN can hand a request to a downstream CDN that is able to serve it.
Like I'm five Different delivery companies agreeing to help each other deliver.
- CDS and CDNSKEY
DNS records a child zone publishes to describe the DS record it wants the parent to hold. The parent can read them to update the delegation's DS records automatically.
Like I'm five Notes the child leaves telling the parent which secret key label to write down.
- CDS and CDNSKEY records
Records a child zone publishes at its apex to tell its parent which DNSSEC key parameters it wants. The parent can use them to create or update the child's DS records.
Like I'm five A note a website leaves for its registry saying which key to use.
- Certificate
A signed document binding a public key to an identity such as a domain name. See RFC 5280.
Like I'm five An ID card for a website, stamped by someone trusted.
Used in RFC 1114 RFC 1422 RFC 1423 RFC 1424 RFC 1507 RFC 1848 RFC 1875 RFC 2094 RFC 2154 RFC 2252 RFC 2311 RFC 2312 RFC 2314 RFC 2315 RFC 2487 RFC 2504 RFC 2511 RFC 2527 RFC 2538 RFC 2559 RFC 2560 RFC 2595 RFC 2631 RFC 2632 and 205 more
An organisation that signs certificates to vouch that a public key belongs to a named server or person. Clients keep a list of CA root keys they trust.
Like I'm five The office that stamps ID cards so other people will believe them.
Used in RFC 1421 RFC 1422 RFC 1424 RFC 1507 RFC 1704 RFC 1848 RFC 1875 RFC 1984 RFC 2312 RFC 2314 RFC 2510 RFC 2511 RFC 2527 RFC 2560 RFC 2585 RFC 2785 RFC 2797 RFC 2818 RFC 2847 RFC 2986 RFC 3039 RFC 3125 RFC 3182 RFC 3193 and 196 more
- Certificate fingerprint
A hash of a certificate, sent in signaling so that a peer can check it against the certificate used in the TLS or DTLS handshake.
Like I'm five A short code that identifies a certificate, like a name tag for a computer.
Used in RFC 4572 RFC 5425 RFC 5763 RFC 7879 RFC 8122 RFC 8842 RFC 8844
- Certificate Management Protocol
CMP is a protocol for enrolling and managing the lifecycle of X.509 certificates between end entities, registration authorities and certification authorities.
Like I'm five The set of rules a device and a certificate office use to ask for, renew and cancel ID cards.
- Certificate Policy
A named set of rules that governs the issuance and management of certificates within a PKI, specifying security requirements, validation procedures, and the assurance levels provided.
Like I'm five A document saying 'this is how we check who you are before we give you an ID card, and how carefully we guard it.'
An organization trusted to issue and sign digital certificates that bind identities to public keys.
Like I'm five A trusted referee who signs papers saying a public key belongs to a certain person.
- Certification path
A chain of certificates leading from a trust anchor to the certificate being checked. A path is valid only if every link passes the validation rules.
Like I'm five The trail of vouching from a trusted authority down to the ID card you are checking.
- Certification Practice Statement
A document that specifies the practices a Certification Authority employs in issuing certificates. It is written to meet the requirements of a Certificate Policy.
Like I'm five A written explanation of exactly how a certificate-issuing group does its job.
- Chain of trust
The alternating DNSKEY and DS record sets in which each link vouches for the next, running from a trust anchor down to the key that signs the data. The RFC calls it the authentication chain.
Like I'm five A line of people each vouching for the next, starting with someone you know.
Used in RFC 1422 RFC 2704 RFC 3090 RFC 3325 RFC 3658 RFC 3779 RFC 4033 RFC 4035 RFC 4081 RFC 4158 RFC 4230 RFC 4641 RFC 4955 RFC 5011 RFC 5074 RFC 5914 RFC 6187 RFC 6481 RFC 6487 RFC 6781 RFC 6841 RFC 6962 RFC 7344 RFC 7646 and 14 more
- Challenge-response
An authentication pattern in which one side issues a challenge and the other replies with credentials that answer it. In HTTP, the 401 response is the challenge and the retried request is the reply.
Like I'm five A guard asks for your ID, and you hold it up.
Used in RFC 1334 RFC 1731 RFC 1760 RFC 1789 RFC 1994 RFC 2095 RFC 2195 RFC 2222 RFC 2289 RFC 2433 RFC 2444 RFC 2617 RFC 2747 RFC 2759 RFC 3012 RFC 3097 RFC 3310 RFC 4256 RFC 4721 RFC 4959 RFC 5090 RFC 5456 RFC 5683 RFC 5906 and 10 more
A RADIUS feature, defined in RFC 5176, that lets a server change or end a user's session after it has started. It covers CoA-Request and Disconnect-Request packets sent to the access server.
Like I'm five A way for the network boss to tell your connection to change its rules or hang up.
- Channel binding
Tying an authentication exchange to the secure channel it runs over, so the two can be shown to belong together.
Like I'm five Proving that the ID check and the private tunnel are really the same conversation.
Used in RFC 2078 RFC 2743 RFC 2744 RFC 4121 RFC 5056 RFC 5247 RFC 5403 RFC 5801 RFC 5802 RFC 5929 RFC 5998 RFC 6677 RFC 6813 RFC 6876 RFC 7055 RFC 7057 RFC 7861 RFC 8353 RFC 8656 RFC 9266
- Channel Hopping
A frequency-diversity technique where transmissions use different frequencies at different times, following a pseudorandom pattern to evade narrow-band interference.
Like I'm five Jumping to a different radio frequency if the current one is noisy, like switching to a different lane if traffic is bad.
- Channel window
The number of bytes one side of an SSH channel may still send before it must wait for permission. The receiver raises it with a window adjust message, and it can never exceed 2^32 - 1 bytes.
Like I'm five A bucket that holds only so much; you can pour in more only after your friend empties it.
- CHAP
The Challenge Handshake Authentication Protocol. A PPP authentication protocol in which the authenticator sends a challenge and the peer answers with a value computed from it and a shared secret. PPP gives it the Protocol value 0xC223.
Like I'm five A guard asks you a changing question that only someone who knows the secret can answer.
Used in RFC 1331 RFC 1471 RFC 1472 RFC 1661 RFC 1994 RFC 2138 RFC 2284 RFC 2341 RFC 2363 RFC 2364 RFC 2433 RFC 2548 RFC 2661 RFC 2759 RFC 2809 RFC 2869 RFC 2989 RFC 3127 RFC 3169 RFC 3720 RFC 3723 RFC 4018 RFC 4545 RFC 4721 and 6 more
- Character set
In MIME, a method of converting a sequence of octets into a sequence of characters, named by the charset parameter, such as US-ASCII or ISO-8859-1.
Like I'm five The code book that says which byte means which letter.
Used in RFC 20 RFC 110 RFC 125 RFC 139 RFC 206 RFC 373 RFC 466 RFC 698 RFC 1345 RFC 1428 RFC 1456 RFC 1468 RFC 1489 RFC 1502 RFC 1554 RFC 1555 RFC 1556 RFC 1557 RFC 1563 RFC 1642 RFC 1815 RFC 1842 RFC 1922 RFC 1942 and 20 more
- Charset
The name of the character set used to turn bytes into letters in a text body, given as a Content-Type parameter such as
charset=iso-8859-1. If it is missing, US-ASCII is assumed.Like I'm five Which alphabet book the writer used, so the reader looks up the right letters.
Used in RFC 1341 RFC 1521 RFC 1522 RFC 1554 RFC 1641 RFC 1815 RFC 1843 RFC 1844 RFC 1874 RFC 1896 RFC 2046 RFC 2047 RFC 2130 RFC 2157 RFC 2277 RFC 2278 RFC 2279 RFC 2295 RFC 2319 RFC 2376 RFC 2426 RFC 2484 RFC 2566 RFC 2652 and 28 more
- Checksum Complement
A 2-octet field at the end of a UDP payload that a device can rewrite after changing other data. Doing so keeps the UDP checksum in the header correct without recomputing it.
Like I'm five A spare note at the end of a message that you adjust so the message's error check still works.
- Checksum-neutral
A modification to data that preserves the Internet checksum value, allowing transport-layer protocols to detect corruption without recalculation after the modification.
Like I'm five A change that doesn't break the error-checking number that TCP or UDP uses.
- Child SA
An ESP or AH Security Association created through an IKE SA. It protects the actual data traffic, and IKE can create, rekey and delete it.
Like I'm five One locked pipe for your real traffic, made using the meeting you already had.
Used in RFC 4555 RFC 4718 RFC 5723 RFC 5857 RFC 5996 RFC 6023 RFC 6311 RFC 7296 RFC 7619 RFC 7791 RFC 8784 RFC 9347 RFC 9370 RFC 9478 RFC 9611 RFC 9867
- Chunk
A basic unit of SDXF data consisting of a header (chunk ID, flags, length) and content. Chunks can be elementary (holding data) or structured (containing other chunks).
Like I'm five A labeled container that holds data or more containers.
- Chunked transfer coding
A way to send a message body in pieces, each preceded by its size in hexadecimal, ending with a zero-size chunk. It lets a sender start transmitting before it knows the total length.
Like I'm five Telling a story in pieces, saying how big each piece is, and saying "zero" at the end.
Used in RFC 2068 RFC 2616 RFC 2910 RFC 3196 RFC 4236 RFC 6202 RFC 7230 RFC 8010 RFC 9112 RFC 9292
- CIDR
Classless Inter-Domain Routing: the system of addressing and routing by prefixes of any length, written a.b.c.d/n, in place of fixed Class A, B and C networks.
Like I'm five It is a way of cutting the Internet's addresses into blocks of whatever size fits.
Used in RFC 1347 RFC 1367 RFC 1375 RFC 1380 RFC 1467 RFC 1481 RFC 1482 RFC 1517 RFC 1518 RFC 1519 RFC 1520 RFC 1656 RFC 1721 RFC 1722 RFC 1752 RFC 1771 RFC 1772 RFC 1773 RFC 1774 RFC 1787 RFC 1812 RFC 1817 RFC 1860 RFC 1878 and 59 more
- Cipher Block Chaining
A mode of operation for block ciphers in which each block is combined with the previous encrypted block before it is encrypted. It starts from an initialization vector (IV).
Like I'm five Each scrambled chunk depends on the chunk before it, like links in a chain.
Used in RFC 1423 RFC 1829 RFC 1851 RFC 2405 RFC 2419 RFC 2420 RFC 2574 RFC 3414 RFC 3602 RFC 4162 RFC 4312 RFC 5932 RFC 6896 RFC 7568
- Cipher suite
In TLS 1.3, a named pair of an AEAD algorithm and a hash algorithm, such as TLS_AES_128_GCM_SHA256. Key exchange and authentication are negotiated separately.
Like I'm five A menu choice that says which lock and which fingerprint method to use.
Used in RFC 1040 RFC 1825 RFC 1827 RFC 1910 RFC 2144 RFC 2179 RFC 2246 RFC 2411 RFC 2523 RFC 2595 RFC 2612 RFC 2712 RFC 2828 RFC 2876 RFC 2910 RFC 2946 RFC 2947 RFC 2948 RFC 2949 RFC 2950 RFC 3268 RFC 3436 RFC 3607 RFC 3749 and 110 more
- Ciphertext Stealing (CTS)
A block cipher mode that encrypts data without ciphertext expansion by rearranging ciphertext blocks of the final partial block, allowing the output to be the same length as the input.
Like I'm five A way to encrypt messages without making them longer, even if the message is not a multiple of the cipher block size.
- Circuit breaker
A last-resort safety mechanism that stops a flow when it suffers persistent excessive congestion. It protects the network and does not replace normal congestion control.
Like I'm five Like a house fuse, it cuts the flow off when it is overloading things.
- Circuit emulation
Making a packet network imitate a fixed-rate circuit, so equipment at each end behaves as if it were joined by a dedicated line.
Like I'm five Making a flexible road act like a private train track.
- Civic address
A location described the way people write addresses, using elements such as country, street, building and room, rather than coordinates.
Like I'm five An address written like on an envelope, not as map coordinates.
- Claim
A name and value pair in a JWT's claims set, such as
iss(issuer) orexp(expiration time). Registered names are defined by the RFC; public and private names are added by applications.Like I'm five One fact written on the note, like "this is for Sam" or "good until Friday".
Used in RFC 7519 RFC 7523 RFC 7800 RFC 8055 RFC 8176 RFC 8225 RFC 8226 RFC 8292 RFC 8392 RFC 8417 RFC 8443 RFC 8485 RFC 8588 RFC 8688 RFC 8693 RFC 8725 RFC 8946 RFC 9027 RFC 9068 RFC 9101 RFC 9118 RFC 9126 RFC 9246 RFC 9470 and 12 more
- Class D address
An IPv4 address whose first four bits are 1110, from 224.0.0.0 to 239.255.255.255. These addresses name multicast groups rather than single hosts.
Like I'm five A club name instead of a person's name.
- Class Selector codepoint
One of the eight DSCPs of the form xxx000. They must map to PHBs that meet the Class Selector requirements, preserving partial compatibility with IP Precedence.
Like I'm five The eight old-style piles that the new system promises to keep working.
- Class-Type
A set of traffic flows that share the same bandwidth constraints and preemption priority rules. Up to eight Class-Types can be defined on a link, each with its own bandwidth allocation.
Like I'm five A category of traffic (like voice or data) that is managed with the same bandwidth rules.
- Classful addressing
The original IPv4 plan in which the first bits of an address fixed the network size: Class A, B or C. CIDR replaced it with explicit prefix lengths.
Like I'm five Only three sizes of house plot were sold, small, medium or enormous.
Used in RFC 791 RFC 796 RFC 917 RFC 940 RFC 943 RFC 952 RFC 990 RFC 997 RFC 1020 RFC 1044 RFC 1117 RFC 1118 RFC 1166 RFC 1338 RFC 1366 RFC 1375 RFC 1466 RFC 1467 RFC 1519 RFC 1606 RFC 1797 RFC 1878 RFC 1879 RFC 1918 and 5 more
- CLAT
The Customer-side Translator, a function in the device that lets IPv4-only applications work over an IPv6-only connection. It relies on a NAT64 in the network.
Like I'm five A little translator inside your phone that helps old apps use the new network.
- Clickjacking
An attack in which a malicious site loads the target site in a transparent frame over dummy buttons, so a click on the visible button actually presses a hidden one, such as an Authorize button.
Like I'm five A hidden button under a fake one, so you press the wrong thing.
- Client
In OAuth, an application that makes requests to protected resources on behalf of the resource owner and with its authorization. The word says nothing about where the application runs.
Like I'm five The app that is asking for permission to use your stuff.
Used in RFC 6749 RFC 6755 RFC 6819 RFC 7009 RFC 7481 RFC 7521 RFC 7522 RFC 7523 RFC 7591 RFC 7592 RFC 7636 RFC 7662 RFC 8252 RFC 8414 RFC 8628 RFC 8693 RFC 8705 RFC 8707 RFC 9101 RFC 9126 RFC 9200 RFC 9201 RFC 9203 RFC 9207 and 4 more
- Client puzzle
A small computational challenge a server hands to a client before doing expensive work. The client needs real effort to solve it, but the server can check the answer cheaply.
Like I'm five A homework problem the server gives you first, so it knows you are serious before it spends effort on you.
- Client-facing server
In ECH, the server that holds the ECH private key and decrypts the outer ClientHello. In split mode it forwards the inner hello to a separate backend server; in shared mode it is the backend server too.
Like I'm five The front desk that opens the sealed envelope, and sometimes passes the letter to someone in the back.
- ClientHello
The first message a TLS client sends in a handshake. It lists what the client supports, and it is where extensions are offered.
Like I'm five The first thing you say when you start a secure chat: "Hi, here is what I can do."
Used in RFC 2818 RFC 4346 RFC 4366 RFC 6066 RFC 7250 RFC 7301 RFC 7465 RFC 7685 RFC 8422 RFC 8446 RFC 8701 RFC 8744 RFC 9146 RFC 9149 RFC 9289 RFC 9846 RFC 9848 RFC 9934
- CLNP
The OSI Connectionless-mode Network Protocol (ISO 8473), the OSI counterpart to IP that carries packets addressed with NSAP addresses.
Like I'm five The old OSI cousin of IP for sending packets.
- Clock discipline
The feedback-loop algorithm that uses NTP's final offset estimate to steer the local system clock's phase and frequency gradually, rather than jumping it.
Like I'm five Gently speeding up or slowing down your clock until it matches.
Used in RFC 32 RFC 958 RFC 1059 RFC 1305 RFC 1589 RFC 5905 RFC 8039 RFC 8173 RFC 9769
- Clock offset
How far one clock is ahead of or behind another. NTP estimates it from four timestamps as half the sum of the two one-way differences.
Like I'm five How many seconds your clock is early or late compared to another clock.
Used in RFC 891 RFC 957 RFC 958 RFC 1059 RFC 1305 RFC 2330 RFC 2679 RFC 2680 RFC 2681 RFC 3393 RFC 3432 RFC 5644 RFC 5905 RFC 7244 RFC 7679 RFC 8039 RFC 8173 RFC 8575 RFC 8877 RFC 9343 RFC 9769 RFC 10030
- Clock skew
The difference between the rate at which a clock runs and the rate of true time or of another clock. Even small skew can introduce large errors when delays are computed from two clocks.
Like I'm five When one clock runs a little faster than another so they slowly drift apart.
- Clos Topology
A folded spine-and-leaf network architecture where leaf nodes connect to spine nodes, which may connect to a higher level of spines (superspines or Top of Fabric). Provides high bisectional bandwidth and natural hierarchy.
Like I'm five A network shaped like a pyramid with leaves at the bottom, spines in the middle, and one or more layers at the top.
- Closest encloser
The longest existing ancestor of a DNS name. NSEC3 responses use it to show where in the name tree a missing name would have to be.
Like I'm five The nearest real folder above a file that is not there.
- Closure alert
A TLS message that tells the peer no more data will be sent on the connection. Receiving one lets an endpoint know a close was not caused by an attacker cutting the connection short.
Like I'm five A polite goodbye that proves the call did not just get cut off.
- Cluster
A group of client routers managed by one or more route reflectors within a routing domain.
Like I'm five A team of routers all served by the same helper.
- CMIP
Common Management Information Protocol; an OSI-based network management protocol intended as an alternative to SNMP, but never widely adopted in TCP/IP networks.
Like I'm five A way to monitor and control network devices using OSI standards, which was less popular than SNMP.
- CMTS
Cable Modem Termination System, the head-end device that connects the cable radio frequency network to the Internet. It assigns and manages service flows for the cable modems it serves.
Like I'm five The big box at the cable company that talks to every modem in the neighborhood.
- CNAME
A DNS record saying that one name is an alias for another name.
Like I'm five A nickname that points to the real name.
Used in RFC 882 RFC 974 RFC 1033 RFC 1279 RFC 1436 RFC 1480 RFC 1535 RFC 1536 RFC 1912 RFC 1985 RFC 2146 RFC 2181 RFC 2219 RFC 2308 RFC 2317 RFC 2535 RFC 2672 RFC 2782 RFC 3550 RFC 3551 RFC 3568 RFC 3861 RFC 4398 RFC 4588 and 39 more
- CoAP
The Constrained Application Protocol, a command and response protocol for microcontrollers with small RAM and ROM, designed for REST-based services.
Like I'm five A lightweight way for tiny gadgets to ask each other for things.
Used in RFC 7641 RFC 7959 RFC 7967 RFC 8075 RFC 8132 RFC 8323 RFC 8516 RFC 8613 RFC 8768 RFC 8824 RFC 8974 RFC 9031 RFC 9132 RFC 9148 RFC 9176 RFC 9177 RFC 9200 RFC 9202 RFC 9244 RFC 9290 RFC 9362 RFC 9430 RFC 9528 RFC 9594 and 4 more
- Code point
A whole number assigned to a character in a coded character set. Unicode code points are written U+ followed by four to six hexadecimal digits, such as U+00FC.
Like I'm five The number that stands for a letter or symbol.
Used in RFC 3260 RFC 3492 RFC 3629 RFC 3692 RFC 3718 RFC 3743 RFC 3987 RFC 4020 RFC 4548 RFC 4940 RFC 5096 RFC 5129 RFC 5137 RFC 5704 RFC 5892 RFC 6365 RFC 6912 RFC 6932 RFC 7120 RFC 7613 RFC 7638 RFC 7670 RFC 7699 RFC 7790 and 16 more
- Codec
A particular way of encoding audio or video for sending. Two endpoints must share at least one codec to exchange media.
Like I'm five A secret language for packing sound or pictures; both sides need to know the same one.
Used in RFC 2658 RFC 3264 RFC 3407 RFC 3551 RFC 3951 RFC 4123 RFC 4298 RFC 4348 RFC 4352 RFC 4424 RFC 5188 RFC 5574 RFC 5577 RFC 6381 RFC 6716 RFC 7205 RFC 7478
- Cofactor
A small divisor of the group order in an elliptic curve. A group with cofactor 1 is prime-order; cofactor > 1 requires special handling in some protocols.
Like I'm five A small divisor that makes the group less clean and requires protocol designers to be extra careful.
- Collation
The process of ordering text units according to language-specific rules, as distinguished from sorting by code point values.
Like I'm five Putting words in alphabetical order, which is different in different languages.
Used in RFC 3381 RFC 3536 RFC 4790 RFC 5051 RFC 5255 RFC 6067 RFC 6365
- Collision attack
An attack that finds two different messages with the same hash value using less work than a perfect hash algorithm would require.
Like I'm five Finding two different things that get the same fingerprint.
- Comfort noise
Artificial background noise played or signalled during silence, so the listener does not think the line has gone dead.
Like I'm five A soft hum played when nobody is talking so you know the call is still there.
- Community string
A name carried in every community-based SNMP message that identifies the community the message belongs to. It acts as the access rule for the message.
Like I'm five A secret word you say to prove you belong to the club.
- Compartment
An application-defined group of messages tied to one peer, such as a session or dialog. State and compressors are kept per compartment, and the application decides when it is created or closed.
Like I'm five A labeled folder where the notes for one conversation are kept.
- Component link
One of the disjoint subsets of resources inside a bundled link. Within a component link, a label alone is enough to identify the resource an LSP uses.
Like I'm five One lane of a multi-lane road.
- Compound object
A document or entity consisting of multiple related components, such as a root document and embedded images or attachments.
Like I'm five A document with multiple pieces, like a webpage with pictures in it.
- Compound RTCP packet
Several RTCP packets sent together in one lower-layer packet. Each compound packet must begin with a Sender Report or Receiver Report.
Like I'm five Putting several letters in one envelope so you only pay for one stamp.
- Compression context
Information about the current compression or decompression state of a flow, such as field values taken from earlier packets.
Like I'm five The memory of what the last packets looked like, used to avoid repeating things.
- Compression dictionary
A body of data known to both compressor and decompressor that acts as a pretend history in front of the data being compressed. It lets small inputs find matches that they would not contain on their own.
Like I'm five A cheat sheet that both sides already have, so they can point at it instead of spelling things out.
- Compression history
The recent data a compressor and decompressor both remember so that repeated sequences can be replaced by short references. Both sides must keep their histories in step.
Like I'm five A notebook of recent messages that both sides keep so they can say see page 3 instead of repeating it.
- Compulsory tunneling
A tunnel that the network sets up for a user without any action or choice by the user, in contrast to voluntary tunneling, where the user creates the tunnel.
Like I'm five A private pipe the network builds for you without asking, instead of one you build yourself.
- Conceptual table
A table of related values in a MIB module, made of rows that each have the same columns. Each row is identified by its index values.
Like I'm five A grid of information, like a class roster with one row per student.
- Conditional request
A request that includes a precondition header such as If-Match, If-None-Match, If-Modified-Since or If-Unmodified-Since, so the server performs the method only if the condition holds.
Like I'm five Saying "only do this if nothing has changed."
Used in RFC 2068 RFC 2227 RFC 3229 RFC 4825 RFC 5023 RFC 5789 RFC 6585 RFC 7162 RFC 7232 RFC 7644 RFC 7808 RFC 8132 RFC 8144 RFC 8182 RFC 8246 RFC 9110 RFC 10008
- Cone NAT
A NAT that maps an internal address and port to the same external address and port for every destination. Restricted variants additionally filter which outside hosts or ports may send packets back in.
Like I'm five A mail room that always gives you the same return box, so anyone you tell can write back.
- Conference blueprint
A conference template that sits at the root of a cloning tree. New conferences can be created by cloning a blueprint and inheriting its attributes.
Like I'm five A ready-made meeting template you copy to start a new meeting.
- Conference focus
The specialised SIP user agent that hosts a conference, processes invitations to it and keeps a SIP dialog with each participant.
Like I'm five The host of a party who lets guests in and keeps track of who is there.
Used in RFC 4245 RFC 4353 RFC 4722 RFC 5239 RFC 7082 RFC 7701
- Conference object
The data that represents a conference at one stage of its life, such as a blueprint, a reservation or an active conference. It is accessed through the conference control protocol.
Like I'm five The fact sheet that describes a meeting and its rules.
- Configuration datastore
A named store of configuration data on a server, such as running, startup or candidate, that management operations can read or edit.
Like I'm five A named shelf where a device keeps one version of its settings.
- Confirming Body
The body that votes to approve or reject candidates proposed by the nominating committee. For IESG candidates, it is the IAB; for IAB candidates, it is the Internet Society Board of Trustees.
Like I'm five The group with the power to say yes or no to the candidates.
- Conformance group
A named collection of related MIB objects or notifications that forms a unit of conformance. An agent that claims a group must implement every item in it.
Like I'm five A labeled box of related items that you either have completely or not at all.
- Confounder
Random data placed in front of a message before it is encrypted, so that using a fixed starting value does not make identical messages look the same.
Like I'm five A few random extra letters stuck on the front so the secret note never looks the same twice.
- Confusable character
A character that looks like another, such as Cyrillic
аand Latina. Confusables can be used to fake names and mislead people.Like I'm five Two different letters that look so alike you cannot tell them apart.
- Congestion collapse
A state in which excess traffic starves other connections of access to the network. Avoiding persistent excessive congestion helps prevent it.
Like I'm five A traffic jam so bad that almost nothing gets through.
Used in RFC 896 RFC 2914 RFC 4336 RFC 5783 RFC 6357 RFC 8084
- Congestion control
The rules, such as slow start, congestion avoidance and exponential backoff of the retransmission timer, that make TCP send more slowly when the network seems overloaded.
Like I'm five Driving slower when the road is jammed so everyone gets through.
Used in RFC 59 RFC 68 RFC 71 RFC 334 RFC 896 RFC 998 RFC 1016 RFC 1018 RFC 1152 RFC 1254 RFC 2001 RFC 2018 RFC 2140 RFC 2309 RFC 2331 RFC 2354 RFC 2357 RFC 2414 RFC 2415 RFC 2416 RFC 2481 RFC 2488 RFC 2581 RFC 2582 and 299 more
- Congestion window
A limit kept by the TCP sender on how much unacknowledged data it may send, set to protect the network from overload. It is often written as cwnd.
Like I'm five A limit on how much you may send so you do not clog the road.
Used in RFC 2001 RFC 2481 RFC 2861 RFC 3042 RFC 3390 RFC 3465 RFC 4015 RFC 5562 RFC 5681 RFC 5827 RFC 7661 RFC 8298 RFC 9406 RFC 9438 RFC 9937 RFC 9959
- Connected Dominating Set
A subset of routers that is connected and is adjacent to every other router. Using it as the relay set lets a flooded packet reach everyone with fewer retransmissions.
Like I'm five A small team of messengers who can reach everyone and also reach each other.
- Connection ID
An identifier that each QUIC endpoint chooses for itself and that appears in packets sent to it. Because packets are matched to a connection by this value rather than by the address and port, a connection can continue after an endpoint's address changes.
Like I'm five A name tag for a conversation that stays the same even if you change seats.
Used in RFC 65 RFC 5154 RFC 8999 RFC 9000 RFC 9146 RFC 9147 RFC 9289 RFC 9528 RFC 9853
- Connection migration
The ability of a QUIC connection to continue after one endpoint's IP address or port changes, for example when a phone moves from Wi-Fi to cellular, by continuing to use the same connection IDs on a new path.
Like I'm five Keeping a phone call going while you walk between rooms.
- Connection preface
The opening bytes each HTTP/2 endpoint sends. The client sends a fixed 24-octet sequence followed by a SETTINGS frame; the server sends a SETTINGS frame.
Like I'm five The special hello that proves both sides really speak HTTP/2.
Used in RFC 9113
- Connectionless
A style of communication where each message is sent independently, with no setup step and no ongoing relationship between sender and receiver.
Like I'm five Dropping a postcard in the mailbox instead of phoning first.
Used in RFC 161 RFC 306 RFC 342 RFC 344 RFC 353 RFC 362 RFC 366 RFC 618 RFC 671 RFC 768 RFC 787 RFC 791 RFC 873 RFC 878 RFC 948 RFC 963 RFC 969 RFC 984 RFC 994 RFC 1005 RFC 1007 RFC 1010 RFC 1086 RFC 1089 and 55 more
- Constrained device
A device with very limited memory, processing power or network capacity, so that every byte sent or stored matters.
Like I'm five A tiny gadget that has very little room for anything.
Used in RFC 6574 RFC 7397 RFC 7452 RFC 7547 RFC 7548 RFC 7744 RFC 7925 RFC 9595
- Constrained Node
A small device with severe limits on power, memory and processing resources, such as a battery-powered sensor.
Like I'm five A tiny gadget that has very little battery and brainpower to spare.
- Constraint-based routing
Routing that computes paths subject to constraints such as bandwidth, hop count, delay and policy. The chosen route is not necessarily the shortest path.
Like I'm five Picking a road that fits your needs, not just the shortest one.
- Container format
A file or stream format that wraps one or more separately encoded media streams together, adding framing and interleaving without changing the encoded data.
Like I'm five A lunchbox that holds several foods together without changing the food.
- Containment tree
The chain of parent links that shows where a physical component sits inside a device, followed upward until a value of zero means nothing contains it.
Like I'm five Like finding which box holds which smaller box, until you reach the biggest box.
- Content Delivery Network
A network of servers distributed globally to serve content to users from locations near them, reducing latency and improving performance.
Like I'm five Copies of popular content stored in different places so you can download from the nearest one.
Used in RFC 3570 RFC 7971 RFC 7975 RFC 8007 RFC 8008 RFC 9538
- Content delivery network
A set of servers that deliver content to users on behalf of content providers. CDNI lets separate CDNs hand traffic to each other.
Like I'm five A group of helper shops spread around that keep copies of things close to you so they arrive fast.
Used in RFC 6707 RFC 6770 RFC 7336 RFC 7337 RFC 7937 RFC 8006 RFC 8586 RFC 8804 RFC 9246 RFC 9677 RFC 9808
- Content Internetworking Gateway
The system through which two content networks exchange request-routing information, distribute content, and share accounting data.
Like I'm five The computer at each network that talks to the other network's computer.
- Content line
One line of an iCalendar object: a name, optional ;PARAM=value parameters, a colon and a value, ended by CRLF.
Like I'm five One line on the card: a label, a colon and an answer.
- Content negotiation
The HTTP mechanism by which a client states its preferences with Accept, Accept-Charset, Accept-Encoding and Accept-Language headers, optionally weighted with q values, and the server chooses the best matching representation of a resource.
Like I'm five Telling the shop what language and size you prefer so it hands you the best one it has.
Used in RFC 2068 RFC 2277 RFC 2295 RFC 2296 RFC 2506 RFC 2533 RFC 2534 RFC 2616 RFC 2703 RFC 2738 RFC 2879 RFC 2912 RFC 2913 RFC 2938 RFC 2987 RFC 3066 RFC 3282 RFC 3297 RFC 3840 RFC 4142 RFC 4647 RFC 5631 RFC 5646 RFC 7089 and 17 more
- Content-Centric Networking
One specific ICN architecture (CCN/CCNx) where content is named hierarchically and requests are forwarded based on content name rather than IP address.
Like I'm five A specific way of building information-centric networks, created at Xerox and later open-sourced.
- Content-encryption key
A random symmetric key that encrypts the content of an enveloped message. It is in turn encrypted separately for each recipient, so the bulk of the data is encrypted only once.
Like I'm five The key to the box, which is itself locked up in a smaller box for each friend.
Used in RFC 2315 RFC 2630 RFC 2876 RFC 2984 RFC 3058 RFC 3185 RFC 3211 RFC 3217 RFC 3218 RFC 3369 RFC 3370 RFC 3537 RFC 3560 RFC 3565 RFC 3851 RFC 3852 RFC 3854 RFC 4010 RFC 4909 RFC 5083 RFC 5091 RFC 5275 RFC 5402 RFC 5408 and 25 more
- Content-Format
A numeric identifier used in CoAP for a Media Type combined with an optional Content Coding. It keeps the label for a payload's format short.
Like I'm five A short number that stands for a kind of data, like a label code on a box.
- Content-ID
A unique identifier header in MIME messages that labels a specific message part or body part. Used by cid: URLs to refer to that part.
Like I'm five A label inside an email that marks one part so other parts can point to it.
- Content-Transfer-Encoding
The MIME header field that says how a body was transformed for transport. Its values are 7bit, 8bit, binary, quoted-printable and base64.
Like I'm five A label saying how the parcel was wrapped to fit through the mail pipe.
Used in RFC 767 RFC 1154 RFC 1341 RFC 1521 RFC 1544 RFC 1554 RFC 1740 RFC 1767 RFC 1847 RFC 2045 RFC 2048 RFC 2049 RFC 2130 RFC 2157 RFC 2159 RFC 2387 RFC 2557 RFC 3156 RFC 3516 RFC 4289 RFC 5524 RFC 6533
- Context
A logical association of multiple Terminations in a Media Gateway, defining the topology—how they connect and exchange media with each other—and any mixing or switching applied.
Like I'm five A group of terminations that are connected together, like the two sides of a phone call.
- Context identifier
A number carried in compressed packets that tells the receiver which stored flow state to use when rebuilding the headers.
Like I'm five A table number that tells the waiter which notes belong to which customer.
Used in RFC 1975 RFC 2507 RFC 2509 RFC 3241 RFC 3544 RFC 3759 RFC 4843 RFC 4901 RFC 5795 RFC 6674
- Context transfer
The movement of service state information from one network node to another as a means of quickly re-establishing services on a new subnet without redoing protocol exchanges from scratch.
Like I'm five Copying a file about you from one place to another so the new place is ready for you right away.
- Control connection
The long-lived TCP connection, on port 21 for FTP, over which the client sends commands and the server sends numbered replies. It follows the Telnet conventions.
Like I'm five The phone line you keep open to talk to the helper.
Used in RFC 2 RFC 114 RFC 354 RFC 542 RFC 959 RFC 1007 RFC 1579 RFC 2228 RFC 2389 RFC 2428 RFC 2577 RFC 2637 RFC 2661 RFC 3659 RFC 4045 RFC 4217 RFC 4454 RFC 4667 RFC 4951 RFC 7121 RFC 8455
- Control Element (CE)
A component in a ForCES network element responsible for control-plane functions such as routing and policy management.
Like I'm five The part that thinks and plans.
Used in RFC 3746 RFC 5810 RFC 5812 RFC 6041 RFC 6369 RFC 6956 RFC 7729
- Control Package
A separate specification that extends the Media Control Channel Framework with the actual commands carried in CONTROL and REPORT messages. It must follow the template given in the framework.
Like I'm five A booklet of orders that the two sides agree to use on their private line.
- Control Plane
The part of a network device that makes decisions about how to handle traffic, such as running routing protocols, applying policies, and managing QoS.
Like I'm five The brain that decides where packets should go.
Used in RFC 3654 RFC 4139 RFC 5920 RFC 6041 RFC 6192 RFC 6583 RFC 7426 RFC 8772 RFC 9673
- Control stream
The single unidirectional stream, identified by stream type 0x00, that each HTTP/3 endpoint opens to carry connection-wide frames such as SETTINGS, GOAWAY and MAX_PUSH_ID.
Like I'm five The walkie-talkie lane for rules about the whole connection.
- Control word
A small header placed after the MPLS labels in a pseudowire packet. It carries protocol control bits and, optionally, a sequence number.
Like I'm five A sticky note on a package with a few quick facts about what is inside.
Used in RFC 547 RFC 4385 RFC 4448 RFC 4618 RFC 4619 RFC 5085 RFC 7079 RFC 8077 RFC 8469
- Convergence
The process by which all routers in a network reach a consistent view of the network topology and compute compatible routing paths.
Like I'm five When all routers agree on how the network looks and where to send traffic.
- Convergence layer
In Delay-Tolerant Networking, an adapter that lets the Bundle Protocol send and receive bundles over some native protocol such as TCP.
Like I'm five A plug adapter that lets one kind of message use whatever road is available.
- Convergence Sublayer
A layer in IEEE 802.16 that maps between the MAC (Media Access Control) layer and upper-layer protocols like IPv6. Different convergence sublayers handle Ethernet or IP differently.
Like I'm five A translator between the wireless network layer and the IP layer.
A small name/value pair, plus scope attributes, that a server asks a user agent to store and return on later matching requests. It is how HTTP, which is otherwise stateless, remembers things between requests.
>Like I'm five A little ticket a website gives your browser so it can recognize you next time.
Used in RFC 1312 RFC 2109 RFC 2409 RFC 2696 RFC 2964 RFC 2965 RFC 3568 RFC 3928 RFC 4306 RFC 4347 RFC 4454 RFC 4555 RFC 4817 RFC 5611 RFC 5971 RFC 5996 RFC 6012 RFC 6013 RFC 6181 RFC 6202 RFC 6265 RFC 6353 RFC 6454 RFC 6462 and 23 more
- COPS
The Common Open Policy Service, a query and response protocol for exchanging policy information between a policy server and its clients.
Like I'm five The language a router uses to ask the policy manager for permission.
- Core router
In CBT, the designated router that acts as the central meeting point for all senders and receivers of a multicast group, similar to a rendezvous point (RP) in other protocols.
Like I'm five The special router in the middle where everyone meets to share messages for a group.
- COSE
CBOR Object Signing and Encryption is a standard way to sign and encrypt CBOR data. CoSWID uses it to protect tags.
Like I'm five A way to put a seal on short coded messages.
Used in RFC 8392 RFC 8613 RFC 8812 RFC 9053 RFC 9360 RFC 9393 RFC 9528 RFC 9711 RFC 9921 RFC 9942 RFC 9964
- Countersignature
A signature made over another signature value rather than over the original content. In CMS it is an unsigned attribute of a SignerInfo.
Like I'm five Signing on top of someone else's signature to show you saw it.
Used in RFC 2315 RFC 2630 RFC 2634 RFC 2649 RFC 2985 RFC 3369 RFC 3852 RFC 5126 RFC 5652 RFC 5752 RFC 5754 RFC 6211 RFC 8702 RFC 9338 RFC 9393 RFC 9688 RFC 9921
- Counting to infinity
A failure mode of distance-vector routing in which routers keep raising the metric of a vanished network by passing it back and forth until it reaches infinity, which is 16 in RIP.
Like I'm five Two friends each say the other knows the way, so the number keeps going up until they give up.
Used in RFC 1009 RFC 1058 RFC 1075 RFC 1164 RFC 2080 RFC 2453
- CR-LDP
Constraint-based routed LDP, defined in RFC 3212. It extends the Label Distribution Protocol so that paths can be set up using extra information such as quality-of-service parameters.
Like I'm five A different way to book a road for your data, built on the label-handing protocol.
- Crankback
A way to recover from a failed path setup by returning to an earlier node and trying another route, instead of giving up at the source straight away.
Like I'm five When a road is blocked, you go back to the last crossroads and try another way.
- CRC32c
A 32-bit cyclic redundancy check used by SCTP to detect damaged packets. It is computed over the common header and the chunks of each packet.
Like I'm five A short number worked out from a message so the receiver can tell if it was scrambled on the way.
- Credit window
A count of octets that a sender is currently allowed to send toward a queue. The sender subtracts what it sends and stops at zero until the receiver grants more.
Like I'm five The number of tickets you have left before you must wait for more.
- Credit-control
A real-time process that checks whether an account has credit, reserves it, deducts what is used and refunds any reserved credit that was not used.
Like I'm five Checking your prepaid balance before you start and subtracting what you really use.
- CRIME attack
An attack in which an observer who sees the length of compressed, encrypted data can learn about the plain data, for example authentication credentials. It is the reason this RFC forbids authentication after compression starts.
Like I'm five Guessing a secret by noticing how big the squashed package is.
- Critical extension
A certificate or CRL extension marked so that software which does not understand it must reject the certificate rather than ignore the extension.
Like I'm five A note on the card that says 'if you cannot read this note, do not accept the card'.
- CRL
Certificate revocation list. A signed list from a CA of certificates that should no longer be trusted before they expire.
Like I'm five A list of ID cards that have been cancelled.
Used in RFC 1421 RFC 1422 RFC 1423 RFC 1424 RFC 2094 RFC 2312 RFC 2315 RFC 2510 RFC 2538 RFC 2559 RFC 2560 RFC 2585 RFC 2587 RFC 2630 RFC 2632 RFC 2692 RFC 3125 RFC 3126 RFC 3161 RFC 3279 RFC 3280 RFC 3379 RFC 3647 RFC 3820 and 73 more
- CRLF
The two-character line ending made of carriage return (
%x0D) followed by line feed (%x0A). RFC 5234 calls it the Internet standard newline.Like I'm five The two invisible letters that tell a computer to start a new line.
Used in RFC 571 RFC 821 RFC 934 RFC 937 RFC 959 RFC 1288 RFC 1413 RFC 1459 RFC 1848 RFC 1870 RFC 1945 RFC 2046 RFC 2060 RFC 2088 RFC 2244 RFC 2812 RFC 2813 RFC 2854 RFC 3501 RFC 3676 RFC 3977 RFC 4037 RFC 4180 RFC 4234 and 5 more
- Cross-certificate
A certificate in which one certification authority vouches for the public key of another authority that is neither its parent nor its child in the naming hierarchy.
Like I'm five A trusted office vouching for another office that is far away in the building.
- Cross-connect
A table entry that links two endpoints of a circuit so that traffic arriving on one is forwarded out of the other. In this MIB a cross-connect row joins a Frame Relay endpoint and an ATM endpoint.
Like I'm five A patch cable that plugs one line into another so the message passes through.
- Cross-Origin Resource Sharing (CORS)
A browser mechanism that lets a server approve exceptions to the same-origin policy. For some requests the browser first sends a preflight request to check for approval.
Like I'm five A permission slip a website must show before your browser lets another website's code talk to it.
- Cross-Site Request Forgery (CSRF)
An attack where a malicious site makes the victim's browser send a request that carries the victim's cookies. Defenses include SameSite cookies, a CORS check with a custom header, and anti-forgery tokens.
Like I'm five Tricking your browser into sending a request you never meant to make.
- Crypto-Binding
A check that ties the key material of an outer tunnel to the inner authentication run inside it. It shows that the same two parties took part in both, which defeats a man in the middle.
Like I'm five A seal that proves the person who came into the hallway is the same person who showed the ID.
- Cryptographic agility
The ability of a protocol to switch to a different cryptographic algorithm without being redesigned. This is usually done by carrying an identifier that says which algorithm is in use.
Like I'm five Being able to swap one lock for a better one without rebuilding the whole door.
- Cryptographic binding
Mixing the keys of an outer tunnel and an inner authentication method into new keys, so that both are proven to end at the same endpoints. It counters tunnel man-in-the-middle attacks.
Like I'm five Tying two locks together so a thief cannot swap one of them.
- Cryptographic hash
A mathematical function that turns a file or message of any size into a fixed-length fingerprint. Two different files will almost certainly produce different hashes, so if a file changes even slightly, its hash changes completely.
Like I'm five A fingerprint for a file that changes if anyone modifies it.
- Cryptographic hash function
A function that maps input of any length onto a fixed-length output. It is meant to be hard to recover the input or to find two different inputs with the same output.
Like I'm five A machine that turns any message into a short fingerprint that is very hard to fake.
- Cryptographic Message Syntax
CMS is a format for signing, authenticating and encrypting data. Content is wrapped in nested layers, each identified by an object identifier.
Like I'm five A way to put a message in nested, labeled envelopes that can be signed or sealed.
Used in RFC 5911 RFC 6010 RFC 7193 RFC 8295 RFC 8769 RFC 9640
- Cryptographic Message Syntax
A standard format for encrypting and signing data, used as the foundation for S/MIME and other secure protocols.
Like I'm five The recipe for how to structure encrypted or signed data so any program can understand it.
Used in RFC 2630 RFC 2797 RFC 3211 RFC 4010 RFC 4108 RFC 4134 RFC 4490 RFC 4556 RFC 5485 RFC 5751 RFC 5754 RFC 5958 RFC 5959 RFC 6019 RFC 6032 RFC 6210 RFC 6211 RFC 6476 RFC 6492 RFC 8358 RFC 8419 RFC 8551 RFC 8572 RFC 8591 and 9 more
- Cryptographic token
The logical view that PKCS #11 gives applications of a device holding cryptographic objects such as keys and certificates. A token sits in a slot.
Like I'm five A small locked box for keys that a program can ask to do secret work.
- Cryptographically Generated Address
An IPv6 address formed by hashing together the subnet prefix, a random nonce and a public key. Signing with the matching private key shows the sender may claim the address.
Like I'm five An address with its owner's fingerprint built into it, so only the owner can prove it is theirs.
- Cryptographically Generated Address
An IPv6 address derived from a public key so that its owner can prove ownership by signing messages with the matching private key. SEND uses these addresses.
Like I'm five An address made from a secret key, so only the key owner can prove it is theirs.
- Cryptography
The science of encoding information in a form that only authorized parties can read, typically using mathematical algorithms and keys.
Like I'm five A way to scramble secrets so only the right person can unscramble them.
- CSIRT
A Computer Security Incident Response Team, a group that handles reports of computer security incidents and helps resolve them for its constituency.
Like I'm five A team of computer emergency responders, like firefighters for security problems.
Used in RFC 2350 RFC 3013 RFC 3067 RFC 5070 RFC 6046 RFC 6545 RFC 7970 RFC 8134
- CSNP (Complete Sequence Number PDU)
A packet that lists all the LSPs a router currently holds, used to synchronize the link state database with neighbors.
Like I'm five A list of "here is everything I have" that neighbors send to help you catch up.
- CSPRNG
A cryptographically secure pseudorandom number generator: a source of random-looking numbers that attackers cannot predict. Good UUIDs of the random kinds should draw from one.
Like I'm five A fair set of dice that nobody can peek at ahead of time.
Used in RFC 8682 RFC 8937 RFC 9562 RFC 9853 RFC 9980 RFC 9986
- CSR (Certificate Signing Request)
A message containing a public key and the names it should be certified for, signed with the matching private key and sent to a certificate authority.
Like I'm five A request form that says: please give me a badge for this name and key.
Used in RFC 2986 RFC 4211 RFC 5272 RFC 5274 RFC 6492 RFC 6955 RFC 7030 RFC 7633 RFC 7894 RFC 7958 RFC 8295 RFC 8555 RFC 8635 RFC 8739 RFC 9115 RFC 9148 RFC 9444 RFC 9448 RFC 9538 RFC 9640 RFC 9642 RFC 9646 RFC 9733 RFC 9763 and 6 more
- CSRC
Contributing source. In RTP, an SSRC of a source that contributed to a stream combined by a mixer; the mixer lists them after the fixed header.
Like I'm five The list of people whose voices were mixed into one.
Used in RFC 1889 RFC 2508 RFC 2862 RFC 3550 RFC 6465 RFC 7656 RFC 7667 RFC 8108 RFC 9071 RFC 9335
- Cursor pagination
A way of splitting a long result list into pages, where the server hands the client an opaque marker that says where the next page begins. The client sends it back to continue.
Like I'm five A bookmark the server gives you so you can continue reading where you stopped.
- Custody transfer
Moving responsibility for reliable delivery of a bundle from one DTN node to another. The node that accepts it is called a custodian and acknowledges with a custody signal.
Like I'm five Handing the parcel to a stop that promises to take care of it from now on.
- Customer Edge (CE)
The customer's own device that connects a customer site to the provider's network, usually through a Provider Edge device.
Like I'm five The customer's plug that connects the office to the phone company.
- Customer Edge router
The router at a customer's home or small office that connects the local network to the Internet service provider.
Like I'm five The box at home that connects your devices to the Internet.
- Customer Premises Equipment
The equipment at the customer edge, such as a home router, that terminates the customer end of an IPv6 transitional tunnel.
Like I'm five The box in your home that connects you to your internet provider.
- Cyclic redundancy check
A small check value computed from data with a polynomial. The receiver recomputes it to detect whether the data was damaged.
Like I'm five A little check number that tells you if something got scrambled on the way.
Used in RFC 935 RFC 1952 RFC 3095 RFC 3720 RFC 4326 RFC 4362 RFC 4815 RFC 5044 RFC 5795 RFC 6846 RFC 9639