Add EVP_PKEY_supports_digest.

This is intended for TLS client auth with Windows CAPI- and CNG-backed keys
which implement sign over sign_raw and do not support all hash functions. Only
plumbed through RSA for now.

Change-Id: Ica42e7fb026840f817a169da9372dda226f7d6fd
Reviewed-on: https://boringssl-review.googlesource.com/2250
Reviewed-by: Adam Langley <agl@google.com>

5 files changed, 20 insertions, 1 deletions

diff --git a/crypto/evp/evp.c b/crypto/evp/evp.c
index c7c4ffbd..ab84b482 100644
--- a/crypto/evp/evp.c
+++ b/crypto/evp/evp.c
@@ -124,6 +124,13 @@ int EVP_PKEY_is_opaque(const EVP_PKEY *pkey) {
   return 0;
 }
 
+int EVP_PKEY_supports_digest(const EVP_PKEY *pkey, const EVP_MD *md) {
+  if (pkey->ameth && pkey->ameth->pkey_supports_digest) {
+    return pkey->ameth->pkey_supports_digest(pkey, md);
+  }
+  return 1;
+}
+
 int EVP_PKEY_cmp(const EVP_PKEY *a, const EVP_PKEY *b) {
   if (a->type != b->type) {
     return -1;
diff --git a/crypto/evp/internal.h b/crypto/evp/internal.h
index ff310e96..2b0f6088 100644
--- a/crypto/evp/internal.h
+++ b/crypto/evp/internal.h
@@ -106,6 +106,12 @@ struct evp_pkey_asn1_method_st {
    * custom implementations which do not expose key material and parameters.*/
   int (*pkey_opaque)(const EVP_PKEY *pk);
 
+  /* pkey_supports_digest returns one if |pkey| supports digests of
+   * type |md|. This is intended for use with EVP_PKEYs backing custom
+   * implementations which can't sign all digests. If null, it is
+   * assumed that all digests are supported. */
+  int (*pkey_supports_digest)(const EVP_PKEY *pkey, const EVP_MD *md);
+
   int (*pkey_size)(const EVP_PKEY *pk);
   int (*pkey_bits)(const EVP_PKEY *pk);
 
diff --git a/crypto/evp/p_ec_asn1.c b/crypto/evp/p_ec_asn1.c
index a423fb88..48a175b2 100644
--- a/crypto/evp/p_ec_asn1.c
+++ b/crypto/evp/p_ec_asn1.c
@@ -555,6 +555,7 @@ const EVP_PKEY_ASN1_METHOD ec_asn1_meth = {
   eckey_priv_print,
 
   eckey_opaque,
+  0 /* pkey_supports_digest */,
 
   int_ec_size,
   ec_bits,
diff --git a/crypto/evp/p_hmac_asn1.c b/crypto/evp/p_hmac_asn1.c
index 06ba0e59..8aa66764 100644
--- a/crypto/evp/p_hmac_asn1.c
+++ b/crypto/evp/p_hmac_asn1.c
@@ -80,7 +80,7 @@ const EVP_PKEY_ASN1_METHOD hmac_asn1_meth = {
     "HMAC",              "OpenSSL HMAC method", 0 /* pub_decode */,
     0 /* pub_encode */,  0 /* pub_cmp */,       0 /* pub_print */,
     0 /*priv_decode */,  0 /* priv_encode */,   0 /* priv_print */,
-    0 /* pkey_opaque */,
+    0 /* pkey_opaque */, 0 /* pkey_supports_digest */,
     hmac_size,           0 /* pkey_bits */,     0 /* param_decode */,
     0 /* param_encode*/, 0 /* param_missing*/,  0 /* param_copy*/,
     0 /* param_cmp*/,    0 /* param_print*/,    0 /* sig_print*/,
diff --git a/crypto/evp/p_rsa_asn1.c b/crypto/evp/p_rsa_asn1.c
index 9c885125..f478d50c 100644
--- a/crypto/evp/p_rsa_asn1.c
+++ b/crypto/evp/p_rsa_asn1.c
@@ -153,6 +153,10 @@ static int rsa_opaque(const EVP_PKEY *pkey) {
   return RSA_is_opaque(pkey->pkey.rsa);
 }
 
+static int rsa_supports_digest(const EVP_PKEY *pkey, const EVP_MD *md) {
+  return RSA_supports_digest(pkey->pkey.rsa, md);
+}
+
 static int int_rsa_size(const EVP_PKEY *pkey) {
   return RSA_size(pkey->pkey.rsa);
 }
@@ -683,6 +687,7 @@ const EVP_PKEY_ASN1_METHOD rsa_asn1_meth = {
   rsa_priv_print,
 
   rsa_opaque,
+  rsa_supports_digest,
 
   int_rsa_size,
   rsa_bits,