Recognize reserved values without giving them meaning
01GREASE reserves deliberately unusable values to exercise handling of unknown capabilities. A codepoint is a number identifying a protocol option.
PskKeyExchangeModes reserves eight distinct byte values. Do not apply the 16-bit pattern to this registry.
Source for this drawing: RFC 8701 · Read RFC section 2 ↗
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A seal answers a specific question.
A certificate or signature supports particular checks about a key or message. It does not automatically prove that every claim or sender is trustworthy.
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Reserved probes are not real capabilities.
- Cipher suites and ALPN identifiers use sixteen repeated-byte pairs, from {0x0A,0x0A} through {0xFA,0xFA}. Hexadecimal notation is a compact way to write bytes.
- Extensions, named groups, signature algorithms and versions use the corresponding sixteen 16-bit values. These cannot be allocated as TLS or DTLS versions.
- PskKeyExchangeModes has a different eight-value list: 0x0B, 0x2A, 0x49, 0x68, 0x87, 0xA6, 0xC5, 0xE4.
ALPN means Application-Layer Protocol Negotiation: peers choose an application protocol such as HTTP. The two-byte GREASE identifiers are byte sequences, not the ASCII text 0A0A. PSK means pre-shared key. GREASE adds no new cipher, group or signature algorithm.
Read the RFC section ↗