[PATCH v5 6/8] lib: rsa: add documentation to padding_pss_verify to document limitations

Heiko Stuebner
2020-05-22T14:19:35Z

padding_pss_verify only works with the default pss salt setting of -2
(length to be automatically determined based on the PSS block structure)
not -1 (salt length set to the maximum permissible value), which makes
verifications of signatures with that saltlen fail.

Until this gets implemented at least document this behaviour.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
---
change in v4:
- new patch

lib/rsa/rsa-verify.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/lib/rsa/rsa-verify.c b/lib/rsa/rsa-verify.c
index 048f1ab789..61d98e6e2d 100644
--- a/lib/rsa/rsa-verify.c
+++ b/lib/rsa/rsa-verify.c
@@ -194,6 +194,19 @@ out:
return ret;
}

+/*
+ * padding_pss_verify() - verify the pss padding of a signature
+ *
+ * Only works with a rsa_pss_saltlen:-2 (default value) right now
+ * saltlen:-1 "set the salt length to the digest length" is currently
+ * not supported.
+ *
+ * @info: Specifies key and FIT information
+ * @msg: byte array of message, len equal to msg_len
+ * @msg_len: Message length
+ * @hash: Pointer to the expected hash
+ * @hash_len: Length of the hash
+ */
int padding_pss_verify(struct image_sign_info *info,
uint8_t *msg, int msg_len,
const uint8_t *hash, int hash_len)
--
2.25.1