diff --git a/src/gsm/kdf/sha256.c b/src/gsm/kdf/sha256.c
new file mode 100644
index 0000000..4f8b6cc
--- /dev/null
+++ b/src/gsm/kdf/sha256.c
@@ -0,0 +1,156 @@
+/*
+ * SHA-256 hash implementation and interface functions
+ * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Alternatively, this software may be distributed under the terms of BSD
+ * license.
+ *
+ * See README and COPYING for more details.
+ */
+
+
+#include "common.h"
+#include "sha256.h"
+#include "crypto.h"
+
+
+/**
+ * hmac_sha256_vector - HMAC-SHA256 over data vector (RFC 2104)
+ * @key: Key for HMAC operations
+ * @key_len: Length of the key in bytes
+ * @num_elem: Number of elements in the data vector
+ * @addr: Pointers to the data areas
+ * @len: Lengths of the data blocks
+ * @mac: Buffer for the hash (32 bytes)
+ */
+void hmac_sha256_vector(const u8 *key, size_t key_len, size_t num_elem,
+			const u8 *addr[], const size_t *len, u8 *mac)
+{
+	unsigned char k_pad[64]; /* padding - key XORd with ipad/opad */
+	unsigned char tk[32];
+	const u8 *_addr[6];
+	size_t _len[6], i;
+
+	if (num_elem > 5) {
+		/*
+		 * Fixed limit on the number of fragments to avoid having to
+		 * allocate memory (which could fail).
+		 */
+		return;
+	}
+
+        /* if key is longer than 64 bytes reset it to key = SHA256(key) */
+        if (key_len > 64) {
+		sha256_vector(1, &key, &key_len, tk);
+		key = tk;
+		key_len = 32;
+        }
+
+	/* the HMAC_SHA256 transform looks like:
+	 *
+	 * SHA256(K XOR opad, SHA256(K XOR ipad, text))
+	 *
+	 * where K is an n byte key
+	 * ipad is the byte 0x36 repeated 64 times
+	 * opad is the byte 0x5c repeated 64 times
+	 * and text is the data being protected */
+
+	/* start out by storing key in ipad */
+	os_memset(k_pad, 0, sizeof(k_pad));
+	os_memcpy(k_pad, key, key_len);
+	/* XOR key with ipad values */
+	for (i = 0; i < 64; i++)
+		k_pad[i] ^= 0x36;
+
+	/* perform inner SHA256 */
+	_addr[0] = k_pad;
+	_len[0] = 64;
+	for (i = 0; i < num_elem; i++) {
+		_addr[i + 1] = addr[i];
+		_len[i + 1] = len[i];
+	}
+	sha256_vector(1 + num_elem, _addr, _len, mac);
+
+	os_memset(k_pad, 0, sizeof(k_pad));
+	os_memcpy(k_pad, key, key_len);
+	/* XOR key with opad values */
+	for (i = 0; i < 64; i++)
+		k_pad[i] ^= 0x5c;
+
+	/* perform outer SHA256 */
+	_addr[0] = k_pad;
+	_len[0] = 64;
+	_addr[1] = mac;
+	_len[1] = SHA256_MAC_LEN;
+	sha256_vector(2, _addr, _len, mac);
+}
+
+
+/**
+ * hmac_sha256 - HMAC-SHA256 over data buffer (RFC 2104)
+ * @key: Key for HMAC operations
+ * @key_len: Length of the key in bytes
+ * @data: Pointers to the data area
+ * @data_len: Length of the data area
+ * @mac: Buffer for the hash (20 bytes)
+ */
+void hmac_sha256(const u8 *key, size_t key_len, const u8 *data,
+		 size_t data_len, u8 *mac)
+{
+	hmac_sha256_vector(key, key_len, 1, &data, &data_len, mac);
+}
+
+
+/**
+ * sha256_prf - SHA256-based Pseudo-Random Function (IEEE 802.11r, 8.5.1.5.2)
+ * @key: Key for PRF
+ * @key_len: Length of the key in bytes
+ * @label: A unique label for each purpose of the PRF
+ * @data: Extra data to bind into the key
+ * @data_len: Length of the data
+ * @buf: Buffer for the generated pseudo-random key
+ * @buf_len: Number of bytes of key to generate
+ *
+ * This function is used to derive new, cryptographically separate keys from a
+ * given key.
+ */
+void sha256_prf(const u8 *key, size_t key_len, const char *label,
+		const u8 *data, size_t data_len, u8 *buf, size_t buf_len)
+{
+	u16 counter = 1;
+	size_t pos, plen;
+	u8 hash[SHA256_MAC_LEN];
+	const u8 *addr[4];
+	size_t len[4];
+	u8 counter_le[2], length_le[2];
+
+	addr[0] = counter_le;
+	len[0] = 2;
+	addr[1] = (u8 *) label;
+	len[1] = os_strlen(label);
+	addr[2] = data;
+	len[2] = data_len;
+	addr[3] = length_le;
+	len[3] = sizeof(length_le);
+
+	WPA_PUT_LE16(length_le, buf_len * 8);
+	pos = 0;
+	while (pos < buf_len) {
+		plen = buf_len - pos;
+		WPA_PUT_LE16(counter_le, counter);
+		if (plen >= SHA256_MAC_LEN) {
+			hmac_sha256_vector(key, key_len, 4, addr, len,
+					   &buf[pos]);
+			pos += SHA256_MAC_LEN;
+		} else {
+			hmac_sha256_vector(key, key_len, 4, addr, len, hash);
+			os_memcpy(&buf[pos], hash, plen);
+			break;
+		}
+		counter++;
+	}
+}