+static void memxor(uint8_t *buf, uint8_t c, size_t len) {
+ for(size_t i = 0; i < len; i++) {
+ buf[i] ^= c;
+ }
+}
+
+static const size_t mdlen = 64;
+static const size_t blklen = 128;
+
+static bool hmac_sha512(const uint8_t *key, size_t keylen, const uint8_t *msg, size_t msglen, uint8_t *out) {
+ uint8_t tmp[blklen + mdlen];
+ sha512_context md;
+
+ if(keylen <= blklen) {
+ memcpy(tmp, key, keylen);
+ memset(tmp + keylen, 0, blklen - keylen);
+ } else {
+ if(sha512(key, keylen, tmp) != 0) {
+ return false;
+ }
+
+ memset(tmp + mdlen, 0, blklen - mdlen);
+ }
+
+ if(sha512_init(&md) != 0) {
+ return false;
+ }
+
+ // ipad
+ memxor(tmp, 0x36, blklen);
+
+ if(sha512_update(&md, tmp, blklen) != 0) {
+ return false;
+ }
+
+ // message
+ if(sha512_update(&md, msg, msglen) != 0) {
+ return false;
+ }
+
+ if(sha512_final(&md, tmp + blklen) != 0) {
+ return false;
+ }
+
+ // opad
+ memxor(tmp, 0x36 ^ 0x5c, blklen);
+
+ if(sha512(tmp, sizeof(tmp), out) != 0) {
+ return false;
+ }
+
+ return true;
+}
+
+
+/* Generate key material from a master secret and a seed, based on RFC 4346 section 5.
+ We use SHA512 instead of MD5 and SHA1.
+ */
+
+bool prf(const uint8_t *secret, size_t secretlen, uint8_t *seed, size_t seedlen, uint8_t *out, size_t outlen) {
+ /* Data is what the "inner" HMAC function processes.
+ It consists of the previous HMAC result plus the seed.
+ */
+
+ uint8_t data[mdlen + seedlen];
+ memset(data, 0, mdlen);
+ memcpy(data + mdlen, seed, seedlen);
+
+ uint8_t hash[mdlen];
+
+ while(outlen > 0) {
+ /* Inner HMAC */
+ if(!hmac_sha512(secret, secretlen, data, sizeof(data), data)) {
+ return false;
+ }
+
+ /* Outer HMAC */
+ if(outlen >= mdlen) {
+ if(!hmac_sha512(secret, secretlen, data, sizeof(data), out)) {
+ return false;
+ }
+
+ out += mdlen;
+ outlen -= mdlen;
+ } else {
+ if(!hmac_sha512(secret, secretlen, data, sizeof(data), hash)) {
+ return false;
+ }
+
+ memcpy(out, hash, outlen);
+ out += outlen;
+ outlen = 0;
+ }
+ }
+
+ return true;