Add helper functions for SSL_SIGN_*.

We end up writing these switch cases everywhere. Let consumers decompose
these a bit. The original thought was folks should write switch-cases so
they handle everything they support, but that's a pain. As long as
algorithm preferences are always configured, we can still add new
dimensions because folks won't be asked to sign algorithms that depend
on dimensions they don't understand.

Change-Id: I3dd7f067f2c55212f0201876546bc70fee032bcf
Reviewed-on: https://boringssl-review.googlesource.com/22524
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Steven Valdez <svaldez@google.com>
diff --git a/ssl/ssl_privkey.cc b/ssl/ssl_privkey.cc
index b00613d..da037d7 100644
--- a/ssl/ssl_privkey.cc
+++ b/ssl/ssl_privkey.cc
@@ -438,6 +438,56 @@
   ctx->cert->key_method = key_method;
 }
 
+const char *SSL_get_signature_algorithm_name(uint16_t sigalg,
+                                             int include_curve) {
+  switch (sigalg) {
+    case SSL_SIGN_RSA_PKCS1_SHA1:
+      return "rsa_pkcs1_sha1";
+    case SSL_SIGN_RSA_PKCS1_SHA256:
+      return "rsa_pkcs1_sha256";
+    case SSL_SIGN_RSA_PKCS1_SHA384:
+      return "rsa_pkcs1_sha384";
+    case SSL_SIGN_RSA_PKCS1_SHA512:
+      return "rsa_pkcs1_sha512";
+    case SSL_SIGN_ECDSA_SHA1:
+      return "ecdsa_sha1";
+    case SSL_SIGN_ECDSA_SECP256R1_SHA256:
+      return include_curve ? "ecdsa_secp256r1_sha256" : "ecdsa_sha256";
+    case SSL_SIGN_ECDSA_SECP384R1_SHA384:
+      return include_curve ? "ecdsa_secp384r1_sha384" : "ecdsa_sha384";
+    case SSL_SIGN_ECDSA_SECP521R1_SHA512:
+      return include_curve ? "ecdsa_secp521r1_sha512" : "ecdsa_sha512";
+    case SSL_SIGN_RSA_PSS_SHA256:
+      return "rsa_pss_sha256";
+    case SSL_SIGN_RSA_PSS_SHA384:
+      return "rsa_pss_sha384";
+    case SSL_SIGN_RSA_PSS_SHA512:
+      return "rsa_pss_sha512";
+    case SSL_SIGN_ED25519:
+      return "ed25519";
+    default:
+      return NULL;
+  }
+}
+
+int SSL_get_signature_algorithm_key_type(uint16_t sigalg) {
+  const SSL_SIGNATURE_ALGORITHM *alg = get_signature_algorithm(sigalg);
+  return alg != nullptr ? alg->pkey_type : EVP_PKEY_NONE;
+}
+
+const EVP_MD *SSL_get_signature_algorithm_digest(uint16_t sigalg) {
+  const SSL_SIGNATURE_ALGORITHM *alg = get_signature_algorithm(sigalg);
+  if (alg == nullptr || alg->digest_func == nullptr) {
+    return nullptr;
+  }
+  return alg->digest_func();
+}
+
+int SSL_is_signature_algorithm_rsa_pss(uint16_t sigalg) {
+  const SSL_SIGNATURE_ALGORITHM *alg = get_signature_algorithm(sigalg);
+  return alg != nullptr && alg->is_rsa_pss;
+}
+
 static int set_algorithm_prefs(uint16_t **out_prefs, size_t *out_num_prefs,
                                const uint16_t *prefs, size_t num_prefs) {
   OPENSSL_free(*out_prefs);