diff --git a/include/libssh/keys.h b/include/libssh/keys.h
index e6354a93..e025b240 100644
--- a/include/libssh/keys.h
+++ b/include/libssh/keys.h
@@ -62,7 +62,6 @@ typedef struct signature_struct {
 
 const char *ssh_type_to_char(int type);
 int ssh_type_from_name(const char *name);
-ssh_buffer ssh_userauth_build_digest(ssh_session session, ssh_message msg, char *service);
 
 ssh_private_key privatekey_make_dss(ssh_session session, ssh_buffer buffer);
 ssh_private_key privatekey_make_rsa(ssh_session session, ssh_buffer buffer,
diff --git a/src/keys.c b/src/keys.c
index 86c4a573..f4e8e2ca 100644
--- a/src/keys.c
+++ b/src/keys.c
@@ -379,70 +379,6 @@ ssh_string ssh_do_sign_with_agent(ssh_session session,
 }
 #endif /* _WIN32 */
 
-/*
- * This function concats in a buffer the values needed to do a signature
- * verification. */
-ssh_buffer ssh_userauth_build_digest(ssh_session session, ssh_message msg, char *service) {
-/*
-     The value of 'signature' is a signature by the corresponding private
-   key over the following data, in the following order:
-
-      string    session identifier
-      byte      SSH_MSG_USERAUTH_REQUEST
-      string    user name
-      string    service name
-      string    "publickey"
-      boolean   TRUE
-      string    public key algorithm name
-      string    public key to be used for authentication
-*/
-	struct ssh_crypto_struct *crypto = session->current_crypto ? session->current_crypto :
-                                             session->next_crypto;
-  ssh_buffer buffer = NULL;
-  ssh_string session_id = NULL;
-  uint8_t type = SSH2_MSG_USERAUTH_REQUEST;
-  ssh_string username = ssh_string_from_char(msg->auth_request.username);
-  ssh_string servicename = ssh_string_from_char(service);
-  ssh_string method = ssh_string_from_char("publickey");
-  uint8_t has_sign = 1;
-  ssh_string algo = ssh_string_from_char(msg->auth_request.public_key->type_c);
-  ssh_string publickey = publickey_to_string(msg->auth_request.public_key);
-
-  buffer = ssh_buffer_new();
-  if (buffer == NULL) {
-    goto error;
-  }
-  session_id = ssh_string_new(SHA_DIGEST_LEN);
-  if (session_id == NULL) {
-    ssh_buffer_free(buffer);
-    buffer = NULL;
-    goto error;
-  }
-  ssh_string_fill(session_id, crypto->session_id, SHA_DIGEST_LEN);
-
-  if(buffer_add_ssh_string(buffer, session_id) < 0 ||
-     buffer_add_u8(buffer, type) < 0 ||
-     buffer_add_ssh_string(buffer, username) < 0 ||
-     buffer_add_ssh_string(buffer, servicename) < 0 ||
-     buffer_add_ssh_string(buffer, method) < 0 ||
-     buffer_add_u8(buffer, has_sign) < 0 ||
-     buffer_add_ssh_string(buffer, algo) < 0 ||
-     buffer_add_ssh_string(buffer, publickey) < 0) {
-    ssh_buffer_free(buffer);
-    buffer = NULL;
-    goto error;
-  }
-
-error:
-  if(session_id) ssh_string_free(session_id);
-  if(username) ssh_string_free(username);
-  if(servicename) ssh_string_free(servicename);
-  if(method) ssh_string_free(method);
-  if(algo) ssh_string_free(algo);
-  if(publickey) ssh_string_free(publickey);
-  return buffer;
-}
-
 /*
  * This function signs the session id (known as H) as a string then
  * the content of sigbuf */
diff --git a/src/messages.c b/src/messages.c
index 30a0fd77..663d8b28 100644
--- a/src/messages.c
+++ b/src/messages.c
@@ -312,6 +312,124 @@ error:
   return SSH_PACKET_USED;
 }
 
+
+/*
+ * This function concats in a buffer the values needed to do a signature
+ * verification.
+ */
+static ssh_buffer ssh_msg_userauth_build_digest(ssh_session session,
+                                                ssh_message msg,
+                                                const char *service)
+{
+    struct ssh_crypto_struct *crypto =
+        session->current_crypto ? session->current_crypto :
+                                  session->next_crypto;
+    ssh_buffer buffer;
+    ssh_string str;
+    int rc;
+
+    buffer = ssh_buffer_new();
+    if (buffer == NULL) {
+        return NULL;
+    }
+
+    /* Add session id */
+    str  = ssh_string_new(SHA_DIGEST_LEN);
+    if (str == NULL) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+    ssh_string_fill(str, crypto->session_id, SHA_DIGEST_LEN);
+
+    rc = buffer_add_ssh_string(buffer, str);
+    string_free(str);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Add the type */
+    rc = buffer_add_u8(buffer, SSH2_MSG_USERAUTH_REQUEST);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Add the username */
+    str = ssh_string_from_char(msg->auth_request.username);
+    if (str == NULL) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+    rc = buffer_add_ssh_string(buffer, str);
+    string_free(str);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Add the service name */
+    str = ssh_string_from_char(service);
+    if (str == NULL) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+    rc = buffer_add_ssh_string(buffer, str);
+    string_free(str);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Add the method (publickey) */
+    str = ssh_string_from_char("publickey");
+    if (str == NULL) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+    rc = buffer_add_ssh_string(buffer, str);
+    string_free(str);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Has been signed (TRUE) */
+    rc = buffer_add_u8(buffer, 1);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Add the public key algorithm */
+    str = ssh_string_from_char(msg->auth_request.public_key->type_c);
+    if (str == NULL) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+    rc = buffer_add_ssh_string(buffer, str);
+    string_free(str);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    /* Add the publickey as blob */
+    str = publickey_to_string(msg->auth_request.public_key);
+    if (str == NULL) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+    rc = buffer_add_ssh_string(buffer, str);
+    string_free(str);
+    if (rc < 0) {
+        ssh_buffer_free(buffer);
+        return NULL;
+    }
+
+    return buffer;
+}
+
 /**
  * @internal
  *
@@ -482,7 +600,7 @@ SSH_PACKET_CALLBACK(ssh_packet_userauth_request){
       }
       signature = signature_from_string(session, sign, public_key,
                                                        public_key->type);
-      digest = ssh_userauth_build_digest(session, msg, service_c);
+      digest = ssh_msg_userauth_build_digest(session, msg, service_c);
       if ((digest == NULL || signature == NULL) ||
           (digest != NULL && signature != NULL &&
           sig_verify(session, public_key, signature,