Annotation of src/usr.bin/ssh/PROTOCOL.krl, Revision 1.5
1.1 djm 1: This describes the key/certificate revocation list format for OpenSSH.
2:
3: 1. Overall format
4:
5: The KRL consists of a header and zero or more sections. The header is:
6:
7: #define KRL_MAGIC 0x5353484b524c0a00ULL /* "SSHKRL\n\0" */
8: #define KRL_FORMAT_VERSION 1
9:
10: uint64 KRL_MAGIC
11: uint32 KRL_FORMAT_VERSION
12: uint64 krl_version
13: uint64 generated_date
14: uint64 flags
15: string reserved
16: string comment
17:
18: Where "krl_version" is a version number that increases each time the KRL
19: is modified, "generated_date" is the time in seconds since 1970-01-01
20: 00:00:00 UTC that the KRL was generated, "comment" is an optional comment
21: and "reserved" an extension field whose contents are currently ignored.
22: No "flags" are currently defined.
23:
24: Following the header are zero or more sections, each consisting of:
25:
26: byte section_type
27: string section_data
28:
29: Where "section_type" indicates the type of the "section_data". An exception
30: to this is the KRL_SECTION_SIGNATURE section, that has a slightly different
31: format (see below).
32:
33: The available section types are:
34:
35: #define KRL_SECTION_CERTIFICATES 1
36: #define KRL_SECTION_EXPLICIT_KEY 2
37: #define KRL_SECTION_FINGERPRINT_SHA1 3
38: #define KRL_SECTION_SIGNATURE 4
1.5 ! djm 39: #define KRL_SECTION_FINGERPRINT_SHA256 5
1.1 djm 40:
1.3 djm 41: 2. Certificate section
1.1 djm 42:
43: These sections use type KRL_SECTION_CERTIFICATES to revoke certificates by
44: serial number or key ID. The consist of the CA key that issued the
45: certificates to be revoked and a reserved field whose contents is currently
46: ignored.
47:
48: string ca_key
49: string reserved
50:
1.3 djm 51: Where "ca_key" is the standard SSH wire serialisation of the CA's
52: public key. Alternately, "ca_key" may be an empty string to indicate
53: the certificate section applies to all CAs (this is most useful when
54: revoking key IDs).
55:
1.1 djm 56: Followed by one or more sections:
57:
58: byte cert_section_type
59: string cert_section_data
60:
61: The certificate section types are:
62:
63: #define KRL_SECTION_CERT_SERIAL_LIST 0x20
64: #define KRL_SECTION_CERT_SERIAL_RANGE 0x21
65: #define KRL_SECTION_CERT_SERIAL_BITMAP 0x22
66: #define KRL_SECTION_CERT_KEY_ID 0x23
67:
68: 2.1 Certificate serial list section
69:
70: This section is identified as KRL_SECTION_CERT_SERIAL_LIST. It revokes
71: certificates by listing their serial numbers. The cert_section_data in this
72: case contains:
73:
74: uint64 revoked_cert_serial
75: uint64 ...
76:
77: This section may appear multiple times.
78:
79: 2.2. Certificate serial range section
80:
81: These sections use type KRL_SECTION_CERT_SERIAL_RANGE and hold
82: a range of serial numbers of certificates:
83:
84: uint64 serial_min
85: uint64 serial_max
86:
87: All certificates in the range serial_min <= serial <= serial_max are
88: revoked.
89:
90: This section may appear multiple times.
91:
92: 2.3. Certificate serial bitmap section
93:
94: Bitmap sections use type KRL_SECTION_CERT_SERIAL_BITMAP and revoke keys
95: by listing their serial number in a bitmap.
96:
97: uint64 serial_offset
98: mpint revoked_keys_bitmap
99:
100: A bit set at index N in the bitmap corresponds to revocation of a keys with
101: serial number (serial_offset + N).
102:
103: This section may appear multiple times.
104:
105: 2.4. Revoked key ID sections
106:
107: KRL_SECTION_CERT_KEY_ID sections revoke particular certificate "key
108: ID" strings. This may be useful in revoking all certificates
109: associated with a particular identity, e.g. a host or a user.
110:
111: string key_id[0]
112: ...
113:
114: This section must contain at least one "key_id". This section may appear
115: multiple times.
116:
117: 3. Explicit key sections
118:
119: These sections, identified as KRL_SECTION_EXPLICIT_KEY, revoke keys
120: (not certificates). They are less space efficient than serial numbers,
121: but are able to revoke plain keys.
122:
123: string public_key_blob[0]
124: ....
125:
126: This section must contain at least one "public_key_blob". The blob
127: must be a raw key (i.e. not a certificate).
128:
129: This section may appear multiple times.
130:
1.5 ! djm 131: 4. SHA1/SHA256 fingerprint sections
1.1 djm 132:
1.5 ! djm 133: These sections, identified as KRL_SECTION_FINGERPRINT_SHA1 and
! 134: KRL_SECTION_FINGERPRINT_SHA256, revoke plain keys (i.e. not
! 135: certificates) by listing their hashes:
1.1 djm 136:
137: string public_key_hash[0]
138: ....
139:
140: This section must contain at least one "public_key_hash". The hash blob
1.5 ! djm 141: is obtained by taking the SHA1 or SHA256 hash of the public key blob.
! 142: Hashes in this section must appear in numeric order, treating each hash
! 143: as a big-endian integer.
1.1 djm 144:
145: This section may appear multiple times.
146:
147: 5. KRL signature sections
148:
149: The KRL_SECTION_SIGNATURE section serves a different purpose to the
1.4 djm 150: preceding ones: to provide cryptographic authentication of a KRL that
1.1 djm 151: is retrieved over a channel that does not provide integrity protection.
152: Its format is slightly different to the previously-described sections:
153: in order to simplify the signature generation, it includes as a "body"
154: two string components instead of one.
155:
156: byte KRL_SECTION_SIGNATURE
157: string signature_key
158: string signature
159:
160: The signature is calculated over the entire KRL from the KRL_MAGIC
161: to this subsection's "signature_key", including both and using the
162: signature generation rules appropriate for the type of "signature_key".
163:
164: This section must appear last in the KRL. If multiple signature sections
165: appear, they must appear consecutively at the end of the KRL file.
166:
167: Implementations that retrieve KRLs over untrusted channels must verify
168: signatures. Signature sections are optional for KRLs distributed by
169: trusted means.
1.2 djm 170:
1.5 ! djm 171: $OpenBSD: PROTOCOL.krl,v 1.4 2018/04/10 00:10:49 djm Exp $
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