ERP: Add HMAC-SHA256 KDF (RFC 5295)

This is needed for ERP key derivation.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/crypto/sha256-kdf.c

@@ -0,0 +1,76 @@
+/*
+ * HMAC-SHA256 KDF (RFC 5295)
+ * Copyright (c) 2014, Jouni Malinen <j@w1.fi>
+ *
+ * This software may be distributed under the terms of the BSD license.
+ * See README for more details.
+ */
+
+#include "includes.h"
+
+#include "common.h"
+#include "sha256.h"
+
+
+/**
+ * hmac_sha256_kdf - HMAC-SHA256 based KDF (RFC 5295)
+ * @secret: Key for KDF
+ * @secret_len: Length of the key in bytes
+ * @label: A unique label for each purpose of the KDF
+ * @seed: Seed value to bind into the key
+ * @seed_len: Length of the seed
+ * @out: Buffer for the generated pseudo-random key
+ * @outlen: Number of bytes of key to generate
+ * Returns: 0 on success, -1 on failure.
+ *
+ * This function is used to derive new, cryptographically separate keys from a
+ * given key in ERP. This KDF is defined in RFC 5295, Chapter 3.1.2.
+ */
+int hmac_sha256_kdf(const u8 *secret, size_t secret_len,
+		    const char *label, const u8 *seed, size_t seed_len,
+		    u8 *out, size_t outlen)
+{
+	u8 T[SHA256_MAC_LEN];
+	u8 iter = 1;
+	const unsigned char *addr[4];
+	size_t len[4];
+	size_t pos, clen;
+
+	addr[0] = T;
+	len[0] = SHA256_MAC_LEN;
+	addr[1] = (const unsigned char *) label;
+	len[1] = os_strlen(label) + 1;
+	addr[2] = seed;
+	len[2] = seed_len;
+	addr[3] = &iter;
+	len[3] = 1;
+
+	if (hmac_sha256_vector(secret, secret_len, 3, &addr[1], &len[1], T) < 0)
+		return -1;
+
+	pos = 0;
+	for (;;) {
+		clen = outlen - pos;
+		if (clen > SHA256_MAC_LEN)
+			clen = SHA256_MAC_LEN;
+		os_memcpy(out + pos, T, clen);
+		pos += clen;
+
+		if (pos == outlen)
+			break;
+
+		if (iter == 255) {
+			os_memset(out, 0, outlen);
+			return -1;
+		}
+		iter++;
+
+		if (hmac_sha256_vector(secret, secret_len, 4, addr, len, T) < 0)
+		{
+			os_memset(out, 0, outlen);
+			return -1;
+		}
+	}
+
+	return 0;
+}

src/crypto/sha256.h

@@ -1,6 +1,6 @@
 /*
  * SHA256 hash implementation and interface functions
- * Copyright (c) 2003-2013, Jouni Malinen <j@w1.fi>
+ * Copyright (c) 2003-2014, Jouni Malinen <j@w1.fi>
  *
  * This software may be distributed under the terms of the BSD license.
  * See README for more details.
@@ -23,5 +23,8 @@ void sha256_prf_bits(const u8 *key, size_t key_len, const char *label,
 void tls_prf_sha256(const u8 *secret, size_t secret_len,
 		    const char *label, const u8 *seed, size_t seed_len,
 		    u8 *out, size_t outlen);
+int hmac_sha256_kdf(const u8 *secret, size_t secret_len,
+		    const char *label, const u8 *seed, size_t seed_len,
+		    u8 *out, size_t outlen);
 
 #endif /* SHA256_H */