This describes the key/certificate revocation list format for OpenSSH.
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1. Overall format
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The KRL consists of a header and zero or more sections. The header is:
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#define KRL_MAGIC 0x5353484b524c0a00ULL /* "SSHKRL\n\0" */
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#define KRL_FORMAT_VERSION 1
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uint64 KRL_MAGIC
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uint32 KRL_FORMAT_VERSION
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uint64 krl_version
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uint64 generated_date
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uint64 flags
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string reserved
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string comment
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Where "krl_version" is a version number that increases each time the KRL
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is modified, "generated_date" is the time in seconds since 1970-01-01
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00:00:00 UTC that the KRL was generated, "comment" is an optional comment
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and "reserved" an extension field whose contents are currently ignored.
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No "flags" are currently defined.
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Following the header are zero or more sections, each consisting of:
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byte section_type
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string section_data
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Where "section_type" indicates the type of the "section_data". An exception
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to this is the KRL_SECTION_SIGNATURE section, that has a slightly different
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format (see below).
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The available section types are:
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#define KRL_SECTION_CERTIFICATES 1
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#define KRL_SECTION_EXPLICIT_KEY 2
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#define KRL_SECTION_FINGERPRINT_SHA1 3
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#define KRL_SECTION_SIGNATURE 4
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2. Certificate section
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These sections use type KRL_SECTION_CERTIFICATES to revoke certificates by
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serial number or key ID. The consist of the CA key that issued the
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certificates to be revoked and a reserved field whose contents is currently
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ignored.
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string ca_key
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string reserved
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Where "ca_key" is the standard SSH wire serialisation of the CA's
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public key. Alternately, "ca_key" may be an empty string to indicate
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the certificate section applies to all CAs (this is most useful when
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revoking key IDs).
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Followed by one or more sections:
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byte cert_section_type
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string cert_section_data
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The certificate section types are:
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#define KRL_SECTION_CERT_SERIAL_LIST 0x20
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#define KRL_SECTION_CERT_SERIAL_RANGE 0x21
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#define KRL_SECTION_CERT_SERIAL_BITMAP 0x22
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#define KRL_SECTION_CERT_KEY_ID 0x23
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2.1 Certificate serial list section
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This section is identified as KRL_SECTION_CERT_SERIAL_LIST. It revokes
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certificates by listing their serial numbers. The cert_section_data in this
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case contains:
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uint64 revoked_cert_serial
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uint64 ...
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This section may appear multiple times.
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2.2. Certificate serial range section
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These sections use type KRL_SECTION_CERT_SERIAL_RANGE and hold
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a range of serial numbers of certificates:
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uint64 serial_min
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uint64 serial_max
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All certificates in the range serial_min <= serial <= serial_max are
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revoked.
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This section may appear multiple times.
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2.3. Certificate serial bitmap section
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Bitmap sections use type KRL_SECTION_CERT_SERIAL_BITMAP and revoke keys
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by listing their serial number in a bitmap.
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uint64 serial_offset
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mpint revoked_keys_bitmap
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A bit set at index N in the bitmap corresponds to revocation of a keys with
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serial number (serial_offset + N).
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This section may appear multiple times.
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2.4. Revoked key ID sections
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KRL_SECTION_CERT_KEY_ID sections revoke particular certificate "key
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ID" strings. This may be useful in revoking all certificates
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associated with a particular identity, e.g. a host or a user.
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string key_id[0]
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...
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This section must contain at least one "key_id". This section may appear
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multiple times.
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3. Explicit key sections
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These sections, identified as KRL_SECTION_EXPLICIT_KEY, revoke keys
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(not certificates). They are less space efficient than serial numbers,
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but are able to revoke plain keys.
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string public_key_blob[0]
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....
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This section must contain at least one "public_key_blob". The blob
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must be a raw key (i.e. not a certificate).
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This section may appear multiple times.
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4. SHA1 fingerprint sections
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These sections, identified as KRL_SECTION_FINGERPRINT_SHA1, revoke
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plain keys (i.e. not certificates) by listing their SHA1 hashes:
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string public_key_hash[0]
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....
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This section must contain at least one "public_key_hash". The hash blob
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is obtained by taking the SHA1 hash of the public key blob. Hashes in
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this section must appear in numeric order, treating each hash as a big-
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endian integer.
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This section may appear multiple times.
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5. KRL signature sections
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The KRL_SECTION_SIGNATURE section serves a different purpose to the
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preceeding ones: to provide cryptographic authentication of a KRL that
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is retrieved over a channel that does not provide integrity protection.
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Its format is slightly different to the previously-described sections:
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in order to simplify the signature generation, it includes as a "body"
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two string components instead of one.
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byte KRL_SECTION_SIGNATURE
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string signature_key
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string signature
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The signature is calculated over the entire KRL from the KRL_MAGIC
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to this subsection's "signature_key", including both and using the
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signature generation rules appropriate for the type of "signature_key".
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This section must appear last in the KRL. If multiple signature sections
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appear, they must appear consecutively at the end of the KRL file.
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Implementations that retrieve KRLs over untrusted channels must verify
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signatures. Signature sections are optional for KRLs distributed by
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trusted means.
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$OpenBSD: PROTOCOL.krl,v 1.3 2015/01/30 01:10:33 djm Exp $
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