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KEYS: X.509: Parse Key Usage

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Parse the X.509 Key Usage.  The key usage extension defines the purpose of
the key contained in the certificate.

   id-ce-keyUsage OBJECT IDENTIFIER ::=  { id-ce 15 }

      KeyUsage ::= BIT STRING {
           digitalSignature        (0),
           contentCommitment       (1),
           keyEncipherment         (2),
           dataEncipherment        (3),
           keyAgreement            (4),
           keyCertSign             (5),
           cRLSign                 (6),
           encipherOnly            (7),
           decipherOnly            (8) }

If the keyCertSign or digitalSignature is set, store it in the
public_key structure. Having the purpose of the key being stored
during parsing, allows enforcement on the usage field in the future.
This will be used in a follow on patch that requires knowing the
certificate key usage type.

Link: https://www.rfc-editor.org/rfc/rfc5280#section-4.2.1.3
Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
This commit is contained in:
Eric Snowberg 2023-03-02 11:46:50 -05:00 committed by Jarkko Sakkinen
parent 30eae2b037
commit 567671281a
2 changed files with 30 additions and 0 deletions
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28
crypto/asymmetric_keys/x509_cert_parser.c
View file

@ -579,6 +579,34 @@ int x509_process_extension(void *context, size_t hdrlen,
return 0;
}
if (ctx->last_oid == OID_keyUsage) {
/*
* Get hold of the keyUsage bit string
* v[1] is the encoding size
* (Expect either 0x02 or 0x03, making it 1 or 2 bytes)
* v[2] is the number of unused bits in the bit string
* (If >= 3 keyCertSign is missing when v[1] = 0x02)
* v[3] and possibly v[4] contain the bit string
*
* From RFC 5280 4.2.1.3:
* 0x04 is where keyCertSign lands in this bit string
* 0x80 is where digitalSignature lands in this bit string
*/
if (v[0] != ASN1_BTS)
return -EBADMSG;
if (vlen < 4)
return -EBADMSG;
if (v[2] >= 8)
return -EBADMSG;
if (v[3] & 0x80)
ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_DIGITALSIG;
if (v[1] == 0x02 && v[2] <= 2 && (v[3] & 0x04))
ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_KEYCERTSIGN;
else if (vlen > 4 && v[1] == 0x03 && (v[3] & 0x04))
ctx->cert->pub->key_eflags |= 1 << KEY_EFLAG_KEYCERTSIGN;
return 0;
}
if (ctx->last_oid == OID_authorityKeyIdentifier) {
/* Get hold of the CA key fingerprint */
ctx->raw_akid = v;

2
include/crypto/public_key.h
View file

@ -30,6 +30,8 @@ struct public_key {
const char *pkey_algo;
unsigned long key_eflags; /* key extension flags */
#define KEY_EFLAG_CA 0 /* set if the CA basic constraints is set */
#define KEY_EFLAG_DIGITALSIG 1 /* set if the digitalSignature usage is set */
#define KEY_EFLAG_KEYCERTSIGN 2 /* set if the keyCertSign usage is set */
};
extern void public_key_free(struct public_key *key);