X-Git-Url: http://git.ozlabs.org/?a=blobdiff_plain;f=ccan%2Fcrypto%2Fhkdf_sha256%2Fhkdf_sha256.c;fp=ccan%2Fcrypto%2Fhkdf_sha256%2Fhkdf_sha256.c;h=0f26485703270c87d51f60f0542e5472f405ac52;hb=33ba12adf082b9432ae0471b6bb742cde14254ed;hp=0000000000000000000000000000000000000000;hpb=ce907a7f849c8cce11083864bf39c84a0f6c7810;p=ccan

diff --git a/ccan/crypto/hkdf_sha256/hkdf_sha256.c b/ccan/crypto/hkdf_sha256/hkdf_sha256.c
new file mode 100644
index 00000000..0f264857
--- /dev/null
+++ b/ccan/crypto/hkdf_sha256/hkdf_sha256.c
@@ -0,0 +1,97 @@
+/* MIT (BSD) license - see LICENSE file for details */
+#include <ccan/crypto/hkdf_sha256/hkdf_sha256.h>
+#include <ccan/crypto/hmac_sha256/hmac_sha256.h>
+#include <assert.h>
+#include <string.h>
+
+void hkdf_sha256(unsigned char *okm, size_t okm_size,
+		 const void *s, size_t ssize,
+		 const void *k, size_t ksize,
+		 const void *info, size_t isize)
+{
+	struct hmac_sha256 prk, t;
+	struct hmac_sha256_ctx ctx;
+	unsigned char c;
+
+	assert(okm_size < 255 * sizeof(t));
+
+	/* RFC 5869:
+	 *
+	 * 2.2.  Step 1: Extract
+	 *
+	 *   HKDF-Extract(salt, IKM) -> PRK
+	 *
+	 *    Options:
+	 *       Hash     a hash function; HashLen denotes the length of the
+	 *                hash function output in octets
+	 *
+	 *    Inputs:
+	 *       salt     optional salt value (a non-secret random value);
+	 *                if not provided, it is set to a string of HashLen zeros.
+	 *       IKM      input keying material
+	 *
+	 *    Output:
+	 *       PRK      a pseudorandom key (of HashLen octets)
+	 *
+	 *    The output PRK is calculated as follows:
+	 *
+	 *    PRK = HMAC-Hash(salt, IKM)
+	 */
+	hmac_sha256(&prk, s, ssize, k, ksize);
+
+	/*
+	 * 2.3.  Step 2: Expand
+	 *
+	 *    HKDF-Expand(PRK, info, L) -> OKM
+	 *
+	 *    Options:
+	 *       Hash     a hash function; HashLen denotes the length of the
+	 *                hash function output in octets
+	 *
+	 *    Inputs:
+	 *       PRK      a pseudorandom key of at least HashLen octets
+	 *                (usually, the output from the extract step)
+	 *       info     optional context and application specific information
+	 *                (can be a zero-length string)
+	 *       L        length of output keying material in octets
+	 *                (<= 255*HashLen)
+	 *
+	 *    Output:
+	 *       OKM      output keying material (of L octets)
+	 *
+	 *    The output OKM is calculated as follows:
+	 *
+	 *    N = ceil(L/HashLen)
+	 *    T = T(1) | T(2) | T(3) | ... | T(N)
+	 *    OKM = first L octets of T
+	 *
+	 *    where:
+	 *    T(0) = empty string (zero length)
+	 *    T(1) = HMAC-Hash(PRK, T(0) | info | 0x01)
+	 *    T(2) = HMAC-Hash(PRK, T(1) | info | 0x02)
+	 *    T(3) = HMAC-Hash(PRK, T(2) | info | 0x03)
+	 *    ...
+	 *
+	 *    (where the constant concatenated to the end of each T(n) is a
+	 *    single octet.)
+	 */
+	c = 1;
+	hmac_sha256_init(&ctx, &prk, sizeof(prk));
+	hmac_sha256_update(&ctx, info, isize);
+	hmac_sha256_update(&ctx, &c, 1);
+	hmac_sha256_done(&ctx, &t);
+
+	while (okm_size > sizeof(t)) {
+		memcpy(okm, &t, sizeof(t));
+		okm += sizeof(t);
+		okm_size -= sizeof(t);
+
+		c++;
+		hmac_sha256_init(&ctx, &prk, sizeof(prk));
+		hmac_sha256_update(&ctx, &t, sizeof(t));
+		hmac_sha256_update(&ctx, info, isize);
+		hmac_sha256_update(&ctx, &c, 1);
+		hmac_sha256_done(&ctx, &t);
+	}
+	memcpy(okm, &t, okm_size);
+}