The SP800-108 compliant Key Derivation Function is implemented as a
random number generator considering that it behaves like a deterministic
RNG.
All three KDF types specified in SP800-108 are implemented.
The code comments provide details about how to invoke the different KDF
types.
Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
---
crypto/kdf.c | 514 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 514 insertions(+)
create mode 100644 crypto/kdf.c
diff --git a/crypto/kdf.c b/crypto/kdf.c
new file mode 100644
index 0000000..b39bddf
--- /dev/null
+++ b/crypto/kdf.c
@@ -0,0 +1,514 @@
+/*
+ * Copyright (C) 2015, Stephan Mueller <smueller@xxxxxxxxxx>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, and the entire permission notice in its entirety,
+ * including the disclaimer of warranties.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ * products derived from this software without specific prior
+ * written permission.
+ *
+ * ALTERNATIVELY, this product may be distributed under the terms of
+ * the GNU General Public License, in which case the provisions of the GPL2
+ * are required INSTEAD OF the above restrictions. (This clause is
+ * necessary due to a potential bad interaction between the GPL and
+ * the restrictions contained in a BSD-style copyright.)
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
+ * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+ * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ */
+
+/*
+ * For performing a KDF operation, the following input is required
+ * from the caller:
+ *
+ * * Keying material to be used to derive the new keys from
+ * (denoted as Ko in SP800-108)
+ * * Label -- a free form binary string
+ * * Context -- a free form binary string
+ *
+ * The KDF is implemented as a random number generator.
+ *
+ * The Ko keying material is to be provided with the initialization of the KDF
+ * "random number generator", i.e. with the crypto_rng_reset function.
+ *
+ * The Label and Context concatenated string is provided when obtaining random
+ * numbers, i.e. with the crypto_rng_generate function. The caller must format
+ * the free-form Label || Context input as deemed necessary for the given
+ * purpose. Note, SP800-108 mandates that the Label and Context are separated
+ * by a 0x00 byte, i.e. the caller shall provide the input as
+ * Label || 0x00 || Context when trying to be compliant to SP800-108. For
+ * the feedback KDF, an IV is required as documented below.
+ *
+ * Example without proper error handling:
+ * char *keying_material = "\x00\x11\x22\x33\x44\x55\x66\x77";
+ * char *label_context = "\xde\xad\xbe\xef\x00\xde\xad\xbe\xef";
+ * kdf = crypto_alloc_rng(name, 0, 0);
+ * crypto_rng_reset(kdf, keying_material, 8);
+ * crypto_rng_generate(kdf, label_context, 9, outbuf, outbuflen);
+ *
+ * NOTE: Technically you can use one buffer for holding the label_context and
+ * the outbuf in the example above. Howerver, multiple rounds of the
+ * KDF are to be expected with the input must always be the same.
+ * The first round would replace the input in case of one buffer, and the
+ * KDF would calculate a cryptographically strong result which, however,
+ * is not portable to other KDF implementations! Thus, always use
+ * different buffers for the label_context and the outbuf. A safe
+ * in-place operation can only be done when only one round of the KDF
+ * is executed (i.e. the size of the requested buffer is equal to the
+ * digestsize of the used MAC).
+ */
+
+#include <linux/module.h>
+#include <crypto/rng.h>
+#include <crypto/hash.h>
+#include <crypto/internal/hash.h>
+
+struct crypto_kdf_ctx {
+ struct shash_desc shash;
+ char ctx[];
+};
+
+/* convert 32 bit integer into its string representation */
+static inline void crypto_kw_cpu_to_be32(u32 val, u8 *buf)
+{
+ __be32 *a = (__be32 *)buf;
+
+ *a = cpu_to_be32(val);
+}
+
+/*
+ * Implementation of the KDF in double pipeline iteration mode according with
+ * counter to SP800-108 section 5.3.
+ *
+ * The caller must provide Label || 0x00 || Context in src. This src pointer
+ * may also be NULL if the caller wishes not to provide anything.
+ */
+static int crypto_kdf_dpi_random(struct crypto_rng *rng,
+ const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int dlen)
+{
+ struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ struct shash_desc *desc = &ctx->shash;
+ unsigned int h = crypto_shash_digestsize(desc->tfm);
+ unsigned int alignmask = crypto_shash_alignmask(desc->tfm);
+ int err = 0;
+ u8 *dst_orig = dst;
+ u8 Aiblock[h + alignmask];
+ u8 *Ai = PTR_ALIGN((u8 *)Aiblock, alignmask + 1);
+ u32 i = 1;
+ u8 iteration[sizeof(u32)];
+
+ /* enforce the note from above */
+ if (dlen != h && src == dst)
+ return -EINVAL;
+
+ memset(Ai, 0, h);
+
+ while (dlen) {
+ /* Calculate A(i) */
+ if (dst == dst_orig && src && slen)
+ /* 5.3 step 4 and 5.a */
+ err = crypto_shash_digest(desc, src, slen, Ai);
+ else
+ /* 5.3 step 5.a */
+ err = crypto_shash_digest(desc, Ai, h, Ai);
+ if (err)
+ goto err;
+
+ /* Calculate K(i) -- step 5.b */
+ err = crypto_shash_init(desc);
+ if (err)
+ goto err;
+
+ err = crypto_shash_update(desc, Ai, h);
+ if (err)
+ goto err;
+
+ crypto_kw_cpu_to_be32(i, iteration);
+ err = crypto_shash_update(desc, iteration, sizeof(u32));
+ if (err)
+ goto err;
+ if (src && slen) {
+ err = crypto_shash_update(desc, src, slen);
+ if (err)
+ goto err;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[h];
+
+ err = crypto_shash_final(desc, tmpbuffer);
+ if (err)
+ goto err;
+ memcpy(dst, tmpbuffer, dlen);
+ memzero_explicit(tmpbuffer, h);
+ goto ret;
+ } else {
+ err = crypto_shash_final(desc, dst);
+ if (err)
+ goto err;
+ dlen -= h;
+ dst += h;
+ i++;
+ }
+ }
+
+err:
+ memzero_explicit(dst_orig, dlen);
+ret:
+ memzero_explicit(Ai, h);
+ return err;
+}
+
+/*
+ * Implementation of the KDF in feedback mode with a non-NULL IV and with
+ * counter according to SP800-108 section 5.2. The IV is supplied with src
+ * and must be equal to the digestsize of the used cipher.
+ *
+ * In addition, the caller must provide Label || 0x00 || Context in src. This
+ * src pointer must not be NULL as the IV is required. The ultimate format of
+ * the src pointer is IV || Label || 0x00 || Context where the length of the
+ * IV is equal to the output size of the PRF.
+ */
+static int crypto_kdf_fb_random(struct crypto_rng *rng,
+ const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int dlen)
+{
+ struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ struct shash_desc *desc = &ctx->shash;
+ unsigned int h = crypto_shash_digestsize(desc->tfm);
+ int err = 0;
+ u8 *dst_orig = dst;
+ const u8 *label;
+ unsigned int labellen = 0;
+ u32 i = 1;
+ u8 iteration[sizeof(u32)];
+
+ /* enforce the note from above */
+ if (dlen != h && src == dst)
+ return -EINVAL;
+
+ /* require the presence of an IV */
+ if (!src || slen < h)
+ return -EINVAL;
+
+ /* calculate the offset of the label / context data */
+ label = src + h;
+ labellen = slen - h;
+
+ while (dlen) {
+ err = crypto_shash_init(desc);
+ if (err)
+ goto err;
+
+ /*
+ * Feedback mode applies to all rounds except first which uses
+ * the IV.
+ */
+ if (dst_orig == dst)
+ err = crypto_shash_update(desc, src, h);
+ else
+ err = crypto_shash_update(desc, dst - h, h);
+ if (err)
+ goto err;
+
+ crypto_kw_cpu_to_be32(i, iteration);
+ err = crypto_shash_update(desc, iteration, sizeof(u32));
+ if (err)
+ goto err;
+ if (labellen) {
+ err = crypto_shash_update(desc, label, labellen);
+ if (err)
+ goto err;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[h];
+
+ err = crypto_shash_final(desc, tmpbuffer);
+ if (err)
+ goto err;
+ memcpy(dst, tmpbuffer, dlen);
+ memzero_explicit(tmpbuffer, h);
+ return 0;
+ } else {
+ err = crypto_shash_final(desc, dst);
+ if (err)
+ goto err;
+ dlen -= h;
+ dst += h;
+ i++;
+ }
+ }
+
+ return 0;
+
+err:
+ memzero_explicit(dst_orig, dlen);
+ return err;
+}
+
+/*
+ * Implementation of the KDF in counter mode according to SP800-108 section 5.1.
+ *
+ * The caller must provide Label || 0x00 || Context in src. This src pointer
+ * may also be NULL if the caller wishes not to provide anything.
+ */
+static int crypto_kdf_ctr_random(struct crypto_rng *rng,
+ const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int dlen)
+{
+ struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ struct shash_desc *desc = &ctx->shash;
+ unsigned int h = crypto_shash_digestsize(desc->tfm);
+ int err = 0;
+ u8 *dst_orig = dst;
+ u32 i = 1;
+ u8 iteration[sizeof(u32)];
+
+ /* enforce the note from above */
+ if (dlen != h && src == dst)
+ return -EINVAL;
+
+ while (dlen) {
+ err = crypto_shash_init(desc);
+ if (err)
+ goto err;
+
+ crypto_kw_cpu_to_be32(i, iteration);
+ err = crypto_shash_update(desc, iteration, sizeof(u32));
+ if (err)
+ goto err;
+
+ if (src && slen) {
+ err = crypto_shash_update(desc, src, slen);
+ if (err)
+ goto err;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[h];
+
+ err = crypto_shash_final(desc, tmpbuffer);
+ if (err)
+ goto err;
+ memcpy(dst, tmpbuffer, dlen);
+ memzero_explicit(tmpbuffer, h);
+ return 0;
+ } else {
+ err = crypto_shash_final(desc, dst);
+ if (err)
+ goto err;
+
+ dlen -= h;
+ dst += h;
+ i++;
+ }
+ }
+
+ return 0;
+
+err:
+ memzero_explicit(dst_orig, dlen);
+ return err;
+}
+
+/*
+ * The seeding of the KDF allows to set a key which must be at least
+ * digestsize long.
+ */
+static int crypto_kdf_seed(struct crypto_rng *rng,
+ const u8 *seed, unsigned int slen)
+{
+ struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ unsigned int ds = crypto_shash_digestsize(ctx->shash.tfm);
+
+ /* Check according to SP800-108 section 7.2 */
+ if (ds > slen)
+ return -EINVAL;
+
+ /*
+ * We require that we operate on a MAC -- if we do not operate on a
+ * MAC, this function returns an error.
+ */
+ return crypto_shash_setkey(ctx->shash.tfm, seed, slen);
+}
+
+static int crypto_kdf_init_tfm(struct crypto_tfm *tfm)
+{
+ struct crypto_instance *inst = crypto_tfm_alg_instance(tfm);
+ struct crypto_shash_spawn *spawn = crypto_instance_ctx(inst);
+ struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(tfm);
+ struct crypto_shash *hash;
+
+ hash = crypto_spawn_shash(spawn);
+ if (IS_ERR(hash))
+ return PTR_ERR(hash);
+
+ ctx->shash.tfm = hash;
+
+ return 0;
+}
+
+static void crypto_kdf_exit_tfm(struct crypto_tfm *tfm)
+{
+ struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(tfm);
+
+ crypto_free_shash(ctx->shash.tfm);
+}
+
+static int crypto_kdf_alloc_common(struct crypto_template *tmpl,
+ struct rtattr **tb,
+ const u8 *name,
+ int (*generate)(struct crypto_rng *tfm,
+ const u8 *src,
+ unsigned int slen,
+ u8 *dst, unsigned int dlen))
+{
+ struct rng_instance *inst;
+ struct crypto_alg *alg;
+ struct shash_alg *salg;
+ int err;
+ unsigned int ds, ss;
+
+ err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_RNG);
+ if (err)
+ return err;
+
+ salg = shash_attr_alg(tb[1], 0, 0);
+ if (IS_ERR(salg))
+ return PTR_ERR(salg);
+
+ ds = salg->digestsize;
+ ss = salg->statesize;
+ alg = &salg->base;
+
+ inst = rng_alloc_instance(name, alg);
+ err = PTR_ERR(inst);
+ if (IS_ERR(inst))
+ goto out_put_alg;
+
+ err = crypto_init_shash_spawn(rng_instance_ctx(inst), salg,
+ rng_crypto_instance(inst));
+ if (err)
+ goto out_free_inst;
+
+ inst->alg.base.cra_priority = alg->cra_priority;
+ inst->alg.base.cra_blocksize = alg->cra_blocksize;
+ inst->alg.base.cra_alignmask = alg->cra_alignmask;
+
+ inst->alg.generate = generate;
+ inst->alg.seed = crypto_kdf_seed;
+ inst->alg.seedsize = ds;
+
+ inst->alg.base.cra_init = crypto_kdf_init_tfm;
+ inst->alg.base.cra_exit = crypto_kdf_exit_tfm;
+ inst->alg.base.cra_ctxsize = ALIGN(sizeof(struct crypto_kdf_ctx) +
+ ss * 2, crypto_tfm_ctx_alignment());
+
+ err = rng_register_instance(tmpl, inst);
+
+ if (err) {
+out_free_inst:
+ rng_free_instance(rng_crypto_instance(inst));
+ }
+
+out_put_alg:
+ crypto_mod_put(alg);
+ return err;
+}
+
+static int crypto_kdf_ctr_create(struct crypto_template *tmpl,
+ struct rtattr **tb)
+{
+ return crypto_kdf_alloc_common(tmpl, tb, "kdf_ctr",
+ crypto_kdf_ctr_random);
+}
+
+static struct crypto_template crypto_kdf_ctr_tmpl = {
+ .name = "kdf_ctr",
+ .create = crypto_kdf_ctr_create,
+ .free = rng_free_instance,
+ .module = THIS_MODULE,
+};
+
+static int crypto_kdf_fb_create(struct crypto_template *tmpl,
+ struct rtattr **tb) {
+ return crypto_kdf_alloc_common(tmpl, tb, "kdf_fb",
+ crypto_kdf_fb_random);
+}
+
+static struct crypto_template crypto_kdf_fb_tmpl = {
+ .name = "kdf_fb",
+ .create = crypto_kdf_fb_create,
+ .free = rng_free_instance,
+ .module = THIS_MODULE,
+};
+
+static int crypto_kdf_dpi_create(struct crypto_template *tmpl,
+ struct rtattr **tb) {
+ return crypto_kdf_alloc_common(tmpl, tb, "kdf_dpi",
+ crypto_kdf_dpi_random);
+}
+
+static struct crypto_template crypto_kdf_dpi_tmpl = {
+ .name = "kdf_dpi",
+ .create = crypto_kdf_dpi_create,
+ .free = rng_free_instance,
+ .module = THIS_MODULE,
+};
+
+static int __init crypto_kdf_init(void)
+{
+ int err = crypto_register_template(&crypto_kdf_ctr_tmpl);
+
+ if (err)
+ return err;
+
+ err = crypto_register_template(&crypto_kdf_fb_tmpl);
+ if (err) {
+ crypto_unregister_template(&crypto_kdf_ctr_tmpl);
+ return err;
+ }
+
+ err = crypto_register_template(&crypto_kdf_dpi_tmpl);
+ if (err) {
+ crypto_unregister_template(&crypto_kdf_ctr_tmpl);
+ crypto_unregister_template(&crypto_kdf_fb_tmpl);
+ }
+ return err;
+}
+
+static void __exit crypto_kdf_exit(void)
+{
+ crypto_unregister_template(&crypto_kdf_ctr_tmpl);
+ crypto_unregister_template(&crypto_kdf_fb_tmpl);
+ crypto_unregister_template(&crypto_kdf_dpi_tmpl);
+}
+
+module_init(crypto_kdf_init);
+module_exit(crypto_kdf_exit);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Stephan Mueller <smueller@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Key Derivation Function according to SP800-108");
+MODULE_ALIAS_CRYPTO("kdf_ctr");
+MODULE_ALIAS_CRYPTO("kdf_fb");
+MODULE_ALIAS_CRYPTO("kdf_dpi");
--
2.7.4
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