Keybase Key IDs (KIDs)

Keybase introduces a new format for public key IDs, inspired by PGP's fingerprint, but: (1) versioned and hence upgradable in the future; (2) based on SHA2 rather than SHA1; and (3) able to accomodate newer cryptosystems like EdDSA without the need for hashing.

The KID format

Version 1 of Keybase KIDs are 35-bytes long, and take the form:

┌──────────┬──────────┬─────────────────────────────────┬──────────────┐
│ version  │ key type │             payload             │ '0a' trailer │
│ (1 byte) │ (1 byte) │           (32 bytes)            │   (1 byte)   │
└──────────┴──────────┴─────────────────────────────────┴──────────────┘

The fields are described as follows:

• version — A 1-byte version number, which is set to 0x01 for version 1. If ever we change the representation of anything below, we'll bump to a new version.

• key type - A 1-byte field describing what type of key we're referring to. Values 0x00 through 0x1f are as in the PGP Spec, RFC 4880, Section 9.1. Most relevant, we have:

  • 0x01 - PGP-style RSA, with PGP-style keys and packets
  • 0x11 - PGP-style DSA, with PGP-style keys and packets

  Values 0x20 and up are for other cryptosystems, that may or may not be specified along with PGP. So far, we have:

  • 0x20 - EdDSA, with Keybase-style packets.
  • 0x21 - DH over Curve25519, with Keybase-style packets.

• payload - For PGP-style keys, this is the SHA-256 of the keymaterial included in the standard PGP fingerprint (see RFC 4880, Section 12.2). For Keybase-style EdDSA and DH over Curve25519, the payload is simply the public key itself, which is 32 bytes in both cases.

• trailer - We append a one-byte trailer to all KIDs, simply the byte 0x0a. Keybase identifiers have a one-byte trailer so that we can distinguish one type of hash from the other by simple inspection. A trailing byte of 0x0a is reserved for KIDs.