dh: Add SSH_PUBLICKEY_HASH_SHA256 to ssh_get_publickey_hash()

Signed-off-by: Jan-Niklas Burfeind <libssh@aiyionpri.me>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/libssh.h

@@ -528,7 +528,8 @@ LIBSSH_API int ssh_get_server_publickey(ssh_session session, ssh_key *key);
 
 enum ssh_publickey_hash_type {
     SSH_PUBLICKEY_HASH_SHA1,
-    SSH_PUBLICKEY_HASH_MD5
+    SSH_PUBLICKEY_HASH_MD5,
+    SSH_PUBLICKEY_HASH_SHA256
 };
 LIBSSH_API int ssh_get_publickey_hash(const ssh_key key,
                                       enum ssh_publickey_hash_type type,

src/dh.c

@@ -1142,6 +1142,29 @@ int ssh_get_publickey_hash(const ssh_key key,
             *hlen = SHA_DIGEST_LEN;
         }
         break;
+    case SSH_PUBLICKEY_HASH_SHA256:
+        {
+            SHA256CTX ctx;
+
+            h = malloc(SHA256_DIGEST_LEN);
+            if (h == NULL) {
+                rc = -1;
+                goto out;
+            }
+
+            ctx = sha256_init();
+            if (ctx == NULL) {
+                free(h);
+                rc = -1;
+                goto out;
+            }
+
+            sha256_update(ctx, ssh_string_data(blob), ssh_string_len(blob));
+            sha256_final(h, ctx);
+
+            *hlen = SHA256_DIGEST_LEN;
+        }
+        break;
     case SSH_PUBLICKEY_HASH_MD5:
         {
             MD5CTX ctx;