crypto/hkdf_sha256: new module.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

ccan/crypto/hkdf_sha256/LICENSE

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+../../../licenses/BSD-MIT

ccan/crypto/hkdf_sha256/_info

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+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * crypto/hkdf_sha256 - RFC5869 Hardened Key Derivation Functions using SHA256
+ *
+ * This code implements the hkdf described in RFC5869.
+ *
+ * License: BSD-MIT
+ * Maintainer: Rusty Russell <rusty@rustcorp.com.au>
+ */
+int main(int argc, char *argv[])
+{
+	/* Expect exactly one argument */
+	if (argc != 2)
+		return 1;
+
+	if (strcmp(argv[1], "depends") == 0) {
+		printf("ccan/crypto/hmac_sha256\n");
+		return 0;
+	}
+
+	if (strcmp(argv[1], "testdepends") == 0) {
+		printf("ccan/str/hex\n");
+		return 0;
+	}
+
+	return 1;
+}

ccan/crypto/hkdf_sha256/hkdf_sha256.c

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+/* 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);
+}

ccan/crypto/hkdf_sha256/hkdf_sha256.h

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+#ifndef CCAN_CRYPTO_HKDF_SHA256_H
+#define CCAN_CRYPTO_HKDF_SHA256_H
+/* BSD-MIT - see LICENSE file for details */
+#include "config.h"
+#include <stdlib.h>
+
+/**
+ * hkdf_sha256 - generate a derived key
+ * @okm: where to output the key
+ * @okm_size: the number of bytes pointed to by @okm (must be less than 255*32)
+ * @s: salt
+ * @ssize: the number of bytes pointed to by @s
+ * @k: pointer to input key
+ * @ksize: the number of bytes pointed to by @k
+ * @info: pointer to info
+ * @isize: the number of bytes pointed to by @info
+ */
+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);
+#endif /* CCAN_CRYPTO_HKDF_SHA256_H */

ccan/crypto/hkdf_sha256/test/api-rfc5869.c

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+/* From RFC5869 Appendix A
+ *
+ * https://tools.ietf.org/html/rfc5869
+ */
+#include <ccan/crypto/hkdf_sha256/hkdf_sha256.h>
+#include <ccan/tap/tap.h>
+#include <ccan/str/hex/hex.h>
+#include <string.h>
+#include <assert.h>
+
+struct test {
+	const char *ikm, *salt, *info, *okm;
+};
+
+static struct test tests[] = { {
+	/* Test Case 1
+	   Basic test case with SHA-256
+	*/
+	"0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b", /* (22 octets) */
+	"000102030405060708090a0b0c", /* (13 octets) */
+	"f0f1f2f3f4f5f6f7f8f9", /* (10 octets) */
+	"3cb25f25faacd57a90434f64d0362f2a2d2d0a90cf1a5a4c5db02d56ecc4c5bf34007208d5b887185865", /* (42 octets) */
+	},
+	{
+	/* Test Case 2
+	 *
+	 * Test with SHA-256 and longer inputs/outputs */
+	"000102030405060708090a0b0c0d0e0f"
+	"101112131415161718191a1b1c1d1e1f"
+	"202122232425262728292a2b2c2d2e2f"
+	"303132333435363738393a3b3c3d3e3f"
+	"404142434445464748494a4b4c4d4e4f", /* (80 octets) */
+	"606162636465666768696a6b6c6d6e6f"
+	"707172737475767778797a7b7c7d7e7f"
+	"808182838485868788898a8b8c8d8e8f"
+	"909192939495969798999a9b9c9d9e9f"
+	"a0a1a2a3a4a5a6a7a8a9aaabacadaeaf", /* (80 octets )*/
+	"b0b1b2b3b4b5b6b7b8b9babbbcbdbebf"
+	"c0c1c2c3c4c5c6c7c8c9cacbcccdcecf"
+	"d0d1d2d3d4d5d6d7d8d9dadbdcdddedf"
+	"e0e1e2e3e4e5e6e7e8e9eaebecedeeef"
+	"f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff", /* (80 octets) */
+	"b11e398dc80327a1c8e7f78c596a4934"
+	"4f012eda2d4efad8a050cc4c19afa97c"
+	"59045a99cac7827271cb41c65e590e09"
+	"da3275600c2f09b8367793a9aca3db71"
+	"cc30c58179ec3e87c14c01d5c1f3434f"
+	"1d87" /* (82 octets) */
+	},
+	{
+	/*  Test Case 3
+	 *
+	 * Test with SHA-256 and zero-length salt/info
+	 */
+	"0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b0b", /* (22 octets) */
+	"", /* (0 octets) */
+	"", /* (0 octets) */
+	"8da4e775a563c18f715f802a063c5a31"
+	"b8a11f5c5ee1879ec3454e5f3c738d2d"
+	"9d201395faa4b61a96c8" /* (42 octets) */
+	}
+};
+
+static void *fromhex(const char *str, size_t *len)
+{
+	void *p;
+
+	*len = hex_data_size(strlen(str));
+	p = malloc(*len);
+	if (!hex_decode(str, strlen(str), p, *len))
+		abort();
+	return p;
+}
+
+int main(void)
+{
+	size_t i;
+
+	plan_tests(sizeof(tests) / sizeof(tests[0]));
+
+	for (i = 0; i < sizeof(tests) / sizeof(tests[0]); i++) {
+		size_t ksize, ssize, isize, okmsize;
+		void *k, *s, *info, *expect, *okm;
+
+		k = fromhex(tests[i].ikm, &ksize);
+		s = fromhex(tests[i].salt, &ssize);
+		info = fromhex(tests[i].info, &isize);
+		expect = fromhex(tests[i].okm, &okmsize);
+		okm = malloc(okmsize);
+		hkdf_sha256(okm, okmsize, s, ssize, k, ksize, info, isize);
+		ok1(memcmp(okm, expect, okmsize) == 0);
+
+		free(k);
+		free(s);
+		free(info);
+		free(expect);
+		free(okm);
+	}
+
+	return exit_status();
+}