Annotation of src/usr.bin/ssh/PROTOCOL.krl, Revision 1.2
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
39:
40: 3. Certificate serial section
41:
42: These sections use type KRL_SECTION_CERTIFICATES to revoke certificates by
43: serial number or key ID. The consist of the CA key that issued the
44: certificates to be revoked and a reserved field whose contents is currently
45: ignored.
46:
47: string ca_key
48: string reserved
49:
50: Followed by one or more sections:
51:
52: byte cert_section_type
53: string cert_section_data
54:
55: The certificate section types are:
56:
57: #define KRL_SECTION_CERT_SERIAL_LIST 0x20
58: #define KRL_SECTION_CERT_SERIAL_RANGE 0x21
59: #define KRL_SECTION_CERT_SERIAL_BITMAP 0x22
60: #define KRL_SECTION_CERT_KEY_ID 0x23
61:
62: 2.1 Certificate serial list section
63:
64: This section is identified as KRL_SECTION_CERT_SERIAL_LIST. It revokes
65: certificates by listing their serial numbers. The cert_section_data in this
66: case contains:
67:
68: uint64 revoked_cert_serial
69: uint64 ...
70:
71: This section may appear multiple times.
72:
73: 2.2. Certificate serial range section
74:
75: These sections use type KRL_SECTION_CERT_SERIAL_RANGE and hold
76: a range of serial numbers of certificates:
77:
78: uint64 serial_min
79: uint64 serial_max
80:
81: All certificates in the range serial_min <= serial <= serial_max are
82: revoked.
83:
84: This section may appear multiple times.
85:
86: 2.3. Certificate serial bitmap section
87:
88: Bitmap sections use type KRL_SECTION_CERT_SERIAL_BITMAP and revoke keys
89: by listing their serial number in a bitmap.
90:
91: uint64 serial_offset
92: mpint revoked_keys_bitmap
93:
94: A bit set at index N in the bitmap corresponds to revocation of a keys with
95: serial number (serial_offset + N).
96:
97: This section may appear multiple times.
98:
99: 2.4. Revoked key ID sections
100:
101: KRL_SECTION_CERT_KEY_ID sections revoke particular certificate "key
102: ID" strings. This may be useful in revoking all certificates
103: associated with a particular identity, e.g. a host or a user.
104:
105: string key_id[0]
106: ...
107:
108: This section must contain at least one "key_id". This section may appear
109: multiple times.
110:
111: 3. Explicit key sections
112:
113: These sections, identified as KRL_SECTION_EXPLICIT_KEY, revoke keys
114: (not certificates). They are less space efficient than serial numbers,
115: but are able to revoke plain keys.
116:
117: string public_key_blob[0]
118: ....
119:
120: This section must contain at least one "public_key_blob". The blob
121: must be a raw key (i.e. not a certificate).
122:
123: This section may appear multiple times.
124:
125: 4. SHA1 fingerprint sections
126:
127: These sections, identified as KRL_SECTION_FINGERPRINT_SHA1, revoke
128: plain keys (i.e. not certificates) by listing their SHA1 hashes:
129:
130: string public_key_hash[0]
131: ....
132:
133: This section must contain at least one "public_key_hash". The hash blob
134: is obtained by taking the SHA1 hash of the public key blob. Hashes in
135: this section must appear in numeric order, treating each hash as a big-
136: endian integer.
137:
138: This section may appear multiple times.
139:
140: 5. KRL signature sections
141:
142: The KRL_SECTION_SIGNATURE section serves a different purpose to the
143: preceeding ones: to provide cryptographic authentication of a KRL that
144: is retrieved over a channel that does not provide integrity protection.
145: Its format is slightly different to the previously-described sections:
146: in order to simplify the signature generation, it includes as a "body"
147: two string components instead of one.
148:
149: byte KRL_SECTION_SIGNATURE
150: string signature_key
151: string signature
152:
153: The signature is calculated over the entire KRL from the KRL_MAGIC
154: to this subsection's "signature_key", including both and using the
155: signature generation rules appropriate for the type of "signature_key".
156:
157: This section must appear last in the KRL. If multiple signature sections
158: appear, they must appear consecutively at the end of the KRL file.
159:
160: Implementations that retrieve KRLs over untrusted channels must verify
161: signatures. Signature sections are optional for KRLs distributed by
162: trusted means.
1.2 ! djm 163:
! 164: $OpenBSD$
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