+#define HMAC_BLOCK_SIZE 64
+
+static void hmac_sha1(unsigned char out[20],
+ const char *key_in, size_t key_len,
+ const char *text, size_t text_len)
+{
+ unsigned char key[HMAC_BLOCK_SIZE];
+ unsigned char k_ipad[HMAC_BLOCK_SIZE];
+ unsigned char k_opad[HMAC_BLOCK_SIZE];
+ int i;
+ git_SHA_CTX ctx;
+
+ /* RFC 2104 2. (1) */
+ memset(key, '\0', HMAC_BLOCK_SIZE);
+ if (HMAC_BLOCK_SIZE < key_len) {
+ git_SHA1_Init(&ctx);
+ git_SHA1_Update(&ctx, key_in, key_len);
+ git_SHA1_Final(key, &ctx);
+ } else {
+ memcpy(key, key_in, key_len);
+ }
+
+ /* RFC 2104 2. (2) & (5) */
+ for (i = 0; i < sizeof(key); i++) {
+ k_ipad[i] = key[i] ^ 0x36;
+ k_opad[i] = key[i] ^ 0x5c;
+ }
+
+ /* RFC 2104 2. (3) & (4) */
+ git_SHA1_Init(&ctx);
+ git_SHA1_Update(&ctx, k_ipad, sizeof(k_ipad));
+ git_SHA1_Update(&ctx, text, text_len);
+ git_SHA1_Final(out, &ctx);
+
+ /* RFC 2104 2. (6) & (7) */
+ git_SHA1_Init(&ctx);
+ git_SHA1_Update(&ctx, k_opad, sizeof(k_opad));
+ git_SHA1_Update(&ctx, out, sizeof(out));
+ git_SHA1_Final(out, &ctx);
+}
+
+static char *prepare_push_cert_nonce(const char *path, unsigned long stamp)
+{
+ struct strbuf buf = STRBUF_INIT;
+ unsigned char sha1[20];
+
+ strbuf_addf(&buf, "%s:%lu", path, stamp);
+ hmac_sha1(sha1, buf.buf, buf.len, cert_nonce_seed, strlen(cert_nonce_seed));;
+ strbuf_release(&buf);
+
+ /* RFC 2104 5. HMAC-SHA1-80 */
+ strbuf_addf(&buf, "%lu-%.*s", stamp, 20, sha1_to_hex(sha1));
+ return strbuf_detach(&buf, NULL);
+}
+
+/*
+ * NEEDSWORK: reuse find_commit_header() from jk/commit-author-parsing
+ * after dropping "_commit" from its name and possibly moving it out
+ * of commit.c
+ */
+static char *find_header(const char *msg, size_t len, const char *key)
+{
+ int key_len = strlen(key);
+ const char *line = msg;
+
+ while (line && line < msg + len) {
+ const char *eol = strchrnul(line, '\n');
+
+ if ((msg + len <= eol) || line == eol)
+ return NULL;
+ if (line + key_len < eol &&
+ !memcmp(line, key, key_len) && line[key_len] == ' ') {
+ int offset = key_len + 1;
+ return xmemdupz(line + offset, (eol - line) - offset);
+ }
+ line = *eol ? eol + 1 : NULL;
+ }
+ return NULL;
+}
+
+static const char *check_nonce(const char *buf, size_t len)
+{
+ char *nonce = find_header(buf, len, "nonce");
+ const char *retval = NONCE_BAD;
+
+ if (!nonce) {
+ retval = NONCE_MISSING;
+ goto leave;
+ } else if (!push_cert_nonce) {
+ retval = NONCE_UNSOLICITED;
+ goto leave;
+ } else if (!strcmp(push_cert_nonce, nonce)) {
+ retval = NONCE_OK;
+ goto leave;
+ }
+
+ /* returned nonce MUST match what we gave out earlier */
+ retval = NONCE_BAD;
+
+leave:
+ free(nonce);
+ return retval;
+}
+