Remove CRT digest from SSL session if !RENEGO + !KEEP_PEER_CERT
If `MBEDTLS_SSL_KEEP_PEER_CERTIFICATE` is not set, `mbedtls_ssl_session`
contains the digest of the peer's certificate for the sole purpose of
detecting a CRT change on renegotiation. Hence, it is not needed if
renegotiation is disabled.
This commit removes the `peer_cert_digest` fields (and friends) from
`mbedtls_ssl_session` if
`!MBEDTLS_SSL_KEEP_PEER_CERTIFICATE + !MBEDTLS_SSL_RENEGOTIATION`,
which is a sensible configuration for constrained devices.
Apart from straightforward replacements of
`if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)`
by
`if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE) && \
defined(MBEDTLS_SSL_RENEGOTIATION)`,
there's one notable change: On the server-side, the CertificateVerify
parsing function is a no-op if the client hasn't sent a certificate.
So far, this was determined by either looking at the peer CRT or the
peer CRT digest in the SSL session structure (depending on the setting
of `MBEDTLS_SSL_KEEP_PEER_CERTIFICATE`), which now no longer works if
`MBEDTLS_SSL_KEEP_PEER_CERTIFICATE` is unset. Instead, this function
now checks whether the temporary copy of the peer's public key within
the handshake structure is initialized or not (which is also a
beneficial simplification in its own right, because the pubkey is
all the function needs anyway).
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 9a36009..eeb03e1 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -856,13 +856,13 @@
#if defined(MBEDTLS_X509_CRT_PARSE_C)
#if defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
mbedtls_x509_crt *peer_cert; /*!< peer X.509 cert chain */
-#else /* MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
+#elif defined(MBEDTLS_SSL_RENEGOTIATION)
/*! The digest of the peer's end-CRT. This must be kept to detect CRT
* changes during renegotiation, mitigating the triple handshake attack. */
unsigned char *peer_cert_digest;
size_t peer_cert_digest_len;
mbedtls_md_type_t peer_cert_digest_type;
-#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
+#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE && MBEDTLS_SSL_RENEGOTIATION */
#endif /* MBEDTLS_X509_CRT_PARSE_C */
uint32_t verify_result; /*!< verification result */