+static int slow_equals(u8 *a, u8 *b, int len)
+{
+ int diff = 0;
+ int i;
+
+ for (i = 0; i < len; i++)
+ diff |= a[i] ^ b[i];
+
+ return diff == 0;
+}
+
+static int passwd_abort(uint64_t etime)
+{
+ const char *sha_env_str = env_get("bootstopkeysha256");
+ u8 sha_env[SHA256_SUM_LEN];
+ u8 sha[SHA256_SUM_LEN];
+ char presskey[MAX_DELAY_STOP_STR];
+ const char *algo_name = "sha256";
+ u_int presskey_len = 0;
+ int abort = 0;
+ int size = sizeof(sha);
+ int ret;
+
+ if (sha_env_str == NULL)
+ sha_env_str = CONFIG_AUTOBOOT_STOP_STR_SHA256;
+
+ /*
+ * Generate the binary value from the environment hash value
+ * so that we can compare this value with the computed hash
+ * from the user input
+ */
+ ret = hash_parse_string(algo_name, sha_env_str, sha_env);
+ if (ret) {
+ printf("Hash %s not supported!\n", algo_name);
+ return 0;
+ }
+
+ /*
+ * We don't know how long the stop-string is, so we need to
+ * generate the sha256 hash upon each input character and
+ * compare the value with the one saved in the environment
+ */
+ do {
+ if (tstc()) {
+ /* Check for input string overflow */
+ if (presskey_len >= MAX_DELAY_STOP_STR)
+ return 0;
+
+ presskey[presskey_len++] = getc();
+
+ /* Calculate sha256 upon each new char */
+ hash_block(algo_name, (const void *)presskey,
+ presskey_len, sha, &size);
+
+ /* And check if sha matches saved value in env */
+ if (slow_equals(sha, sha_env, SHA256_SUM_LEN))
+ abort = 1;
+ }
+ } while (!abort && get_ticks() <= etime);
+
+ return abort;
+}
+#else
+static int passwd_abort(uint64_t etime)