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Annotation of src/usr.bin/ssh/PROTOCOL.key, Revision 1.2

1.1       markus      1: This document describes the private key format for OpenSSH.
                      2:
                      3: 1. Overall format
                      4:
                      5: The key consists of a header, a list of public keys, and
                      6: an encrypted list of matching private keys.
                      7:
                      8: #define AUTH_MAGIC      "openssh-key-v1"
                      9:
                     10:        byte[]  AUTH_MAGIC
                     11:        string  ciphername
                     12:        string  kdfname
                     13:        string  kdfoptions
                     14:        int     number of keys N
                     15:        string  publickey1
                     16:        string  publickey2
                     17:        ...
                     18:        string  publickeyN
                     19:        string  encrypted, padded list of private keys
                     20:
                     21: 2. KDF options for kdfname "bcrypt"
                     22:
                     23: The options:
                     24:
                     25:        string salt
                     26:        uint32 rounds
                     27:
                     28: are concatenated and represented as a string.
                     29:
                     30: 3. Unencrypted list of N private keys
                     31:
                     32: The list of privatekey/comment pairs is padded with the
                     33: bytes 1, 2, 3, ... until the total length is a multiple
                     34: of the cipher block size.
                     35:
                     36:        uint32  checkint
                     37:        uint32  checkint
1.2     ! djm        38:        byte[]  privatekey1
1.1       markus     39:        string  comment1
1.2     ! djm        40:        byte[]  privatekey2
1.1       markus     41:        string  comment2
                     42:        ...
                     43:        string  privatekeyN
                     44:        string  commentN
                     45:        char    1
                     46:        char    2
                     47:        char    3
                     48:        ...
                     49:        char    padlen % 255
                     50:
1.2     ! djm        51: where each private key is encoded using the same rules as used for
        !            52: SSH agent.
        !            53:
1.1       markus     54: Before the key is encrypted, a random integer is assigned
                     55: to both checkint fields so successful decryption can be
                     56: quickly checked by verifying that both checkint fields
                     57: hold the same value.
                     58:
                     59: 4. Encryption
                     60:
                     61: The KDF is used to derive a key, IV (and other values required by
                     62: the cipher) from the passphrase. These values are then used to
                     63: encrypt the unencrypted list of private keys.
                     64:
                     65: 5. No encryption
                     66:
                     67: For unencrypted keys the cipher "none" and the KDF "none"
                     68: are used with empty passphrases. The options if the KDF "none"
                     69: are the empty string.
                     70:
1.2     ! djm        71: $OpenBSD: PROTOCOL.key,v 1.1 2013/12/06 13:34:54 markus Exp $