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@xxxxxxxxxx>
Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
crypto/asymmetric_keys/x509_cert_parser.c | 28 +++++++++++++++++++++++
include/crypto/public_key.h | 2 ++
2 files changed, 30 insertions(+)
diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 77547d4bd94d..0a7049b470c1 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -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;
diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
index c401762850f2..03c3fb990d59 100644
--- a/include/crypto/public_key.h
+++ b/include/crypto/public_key.h
@@ -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);
--
2.27.0
