[PATCH v2 2/6] crypto: kdf - SP800-108 Key Derivation Function

Stephan Müller
2019-01-16T11:12:18Z

The SP800-108 compliant Key Derivation Function provides three KDF
types which are all implemented, including the counter-based KDF,
the double-pipeline KDF and the feedback KDF.

The code comments provide details about how to invoke the different KDF
types.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
crypto/Kconfig | 7 +
crypto/Makefile | 1 +
crypto/kdf_sp800108.c | 491 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 499 insertions(+)
create mode 100644 crypto/kdf_sp800108.c

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 86960aa53e0f..7c0336c9ba9c 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -561,6 +561,13 @@ config CRYPTO_HMAC
HMAC: Keyed-Hashing for Message Authentication (RFC2104).
This is required for IPSec.

+config CRYPTO_KDF_SP800108
+ tristate "Key Derivation Function (SP800-108)"
+ select CRYPTO_RNG
+ help
+ Support for KDF compliant to SP800-108. All three types of
+ KDF specified in SP800-108 are implemented.
+
config CRYPTO_XCBC
tristate "XCBC support"
select CRYPTO_HASH
diff --git a/crypto/Makefile b/crypto/Makefile
index 799ed5e94606..eead7ec9fd8e 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -58,6 +58,7 @@ crypto_user-y := crypto_user_base.o
crypto_user-$(CONFIG_CRYPTO_STATS) += crypto_user_stat.o
obj-$(CONFIG_CRYPTO_CMAC) += cmac.o
obj-$(CONFIG_CRYPTO_HMAC) += hmac.o
+obj-$(CONFIG_CRYPTO_KDF_SP800108) += kdf_sp800108.o
obj-$(CONFIG_CRYPTO_VMAC) += vmac.o
obj-$(CONFIG_CRYPTO_XCBC) += xcbc.o
obj-$(CONFIG_CRYPTO_NULL2) += crypto_null.o
diff --git a/crypto/kdf_sp800108.c b/crypto/kdf_sp800108.c
new file mode 100644
index 000000000000..33b26659afa7
--- /dev/null
+++ b/crypto/kdf_sp800108.c
@@ -0,0 +1,491 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * SP800-108 Key-derivation function
+ *
+ * Copyright (C) 2019, Stephan Mueller <smueller@chronox.de>
+ */
+
+/*
+ * 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);
+ */
+
+#include <linux/module.h>
+#include <crypto/rng.h>
+#include <crypto/internal/rng.h>
+#include <crypto/hash.h>
+#include <crypto/internal/hash.h>
+
+struct crypto_kdf_ctx {
+ struct crypto_shash *kmd;
+};
+
+#define CRYPTO_KDF_MAX_DIGESTSIZE 64
+#define CRYPTO_KDF_MAX_ALIGNMASK 0x3f
+
+static inline void crypto_kdf_init_desc(struct shash_desc *desc,
+ struct crypto_shash *kmd)
+{
+ desc->tfm = kmd;
+ desc->flags = 0;
+}
+
+/*
+ * 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_generate(struct crypto_rng *rng,
+ const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int dlen)
+{
+ const struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ struct crypto_shash *kmd = ctx->kmd;
+ SHASH_DESC_ON_STACK(desc, kmd);
+ __be32 counter = cpu_to_be32(1);
+ const unsigned int h = crypto_shash_digestsize(kmd);
+ const unsigned int alignmask = crypto_shash_alignmask(kmd);
+ int err = 0;
+ u8 *dst_orig = dst;
+ u8 Aiblock[CRYPTO_KDF_MAX_DIGESTSIZE + CRYPTO_KDF_MAX_ALIGNMASK];
+ u8 *Ai = PTR_ALIGN((u8 *)Aiblock, alignmask + 1);
+
+ crypto_kdf_init_desc(desc, kmd);
+
+ 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 out;
+
+ /* Calculate K(i) -- step 5.b */
+ err = crypto_shash_init(desc);
+ if (err)
+ goto out;
+
+ err = crypto_shash_update(desc, Ai, h);
+ if (err)
+ goto out;
+
+ err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
+ if (err)
+ goto out;
+ if (src && slen) {
+ err = crypto_shash_update(desc, src, slen);
+ if (err)
+ goto out;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[CRYPTO_KDF_MAX_DIGESTSIZE];
+
+ err = crypto_shash_final(desc, tmpbuffer);
+ if (err)
+ goto out;
+ memcpy(dst, tmpbuffer, dlen);
+ memzero_explicit(tmpbuffer, h);
+ goto out;
+ }
+
+ err = crypto_shash_final(desc, dst);
+ if (err)
+ goto out;
+ dlen -= h;
+ dst += h;
+ counter = cpu_to_be32(be32_to_cpu(counter) + 1);
+ }
+
+out:
+ if (err)
+ memzero_explicit(dst_orig, dlen);
+ shash_desc_zero(desc);
+ 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 keyed message digest.
+ *
+ * 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_generate(struct crypto_rng *rng,
+ const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int dlen)
+{
+ const struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ struct crypto_shash *kmd = ctx->kmd;
+ SHASH_DESC_ON_STACK(desc, kmd);
+ __be32 counter = cpu_to_be32(1);
+ const unsigned int h = crypto_shash_digestsize(kmd);
+ unsigned int labellen = 0;
+ int err = 0;
+ u8 *dst_orig = dst;
+ const u8 *label;
+
+ /* require the presence of an IV */
+ if (!src || slen < h)
+ return -EINVAL;
+
+ crypto_kdf_init_desc(desc, kmd);
+
+ /* calculate the offset of the label / context data */
+ label = src + h;
+ labellen = slen - h;
+
+ while (dlen) {
+ err = crypto_shash_init(desc);
+ if (err)
+ goto out;
+
+ /*
+ * 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 out;
+
+ err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
+ if (err)
+ goto out;
+ if (labellen) {
+ err = crypto_shash_update(desc, label, labellen);
+ if (err)
+ goto out;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[CRYPTO_KDF_MAX_DIGESTSIZE];
+
+ err = crypto_shash_final(desc, tmpbuffer);
+ if (err)
+ goto out;
+ memcpy(dst, tmpbuffer, dlen);
+ memzero_explicit(tmpbuffer, h);
+ goto out;
+ }
+
+ err = crypto_shash_final(desc, dst);
+ if (err)
+ goto out;
+ dlen -= h;
+ dst += h;
+ counter = cpu_to_be32(be32_to_cpu(counter) + 1);
+ }
+
+out:
+ if (err)
+ memzero_explicit(dst_orig, dlen);
+ return err;
+}
+
+/*
+ * Implementation of the KDF in counter mode according to SP800-108 section 5.1
+ * as well as SP800-56A section 5.8.1 (Single-step KDF).
+ *
+ * SP800-108:
+ * The caller must provide Label || 0x00 || Context in src. This src pointer
+ * may also be NULL if the caller wishes not to provide anything.
+ *
+ * SP800-56A:
+ * The key provided for the HMAC during the crypto_rng_reset shall NOT be the
+ * shared secret from the DH operation, but an independently generated key.
+ * The src pointer is defined as Z || other info where Z is the shared secret
+ * from DH and other info is an arbitrary string (see SP800-56A section
+ * 5.8.1.2).
+ */
+static int crypto_kdf_ctr_generate(struct crypto_rng *rng,
+ const u8 *src, unsigned int slen,
+ u8 *dst, unsigned int dlen)
+{
+ const struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ struct crypto_shash *kmd = ctx->kmd;
+ SHASH_DESC_ON_STACK(desc, kmd);
+ __be32 counter = cpu_to_be32(1);
+ const unsigned int h = crypto_shash_digestsize(kmd);
+ int err = 0;
+ u8 *dst_orig = dst;
+
+ crypto_kdf_init_desc(desc, kmd);
+
+ while (dlen) {
+ err = crypto_shash_init(desc);
+ if (err)
+ goto out;
+
+ err = crypto_shash_update(desc, (u8 *)&counter, sizeof(__be32));
+ if (err)
+ goto out;
+
+ if (src && slen) {
+ err = crypto_shash_update(desc, src, slen);
+ if (err)
+ goto out;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[CRYPTO_KDF_MAX_DIGESTSIZE];
+
+ err = crypto_shash_final(desc, tmpbuffer);
+ if (err)
+ goto out;
+ memcpy(dst, tmpbuffer, dlen);
+ memzero_explicit(tmpbuffer, h);
+ return 0;
+ }
+
+ err = crypto_shash_final(desc, dst);
+ if (err)
+ goto out;
+
+ dlen -= h;
+ dst += h;
+ counter = cpu_to_be32(be32_to_cpu(counter) + 1);
+ }
+
+out:
+ if (err)
+ memzero_explicit(dst_orig, dlen);
+ shash_desc_zero(desc);
+ 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)
+{
+ const struct crypto_kdf_ctx *ctx = crypto_tfm_ctx(crypto_rng_tfm(rng));
+ unsigned int ds = crypto_shash_digestsize(ctx->kmd);
+
+ /* 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->kmd, 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 *kmd;
+
+ kmd = crypto_spawn_shash(spawn);
+ if (IS_ERR(kmd))
+ return PTR_ERR(kmd);
+
+ ctx->kmd = kmd;
+
+ 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->kmd);
+}
+
+static void crypto_kdf_free(struct rng_instance *inst)
+{
+ crypto_drop_spawn(rng_instance_ctx(inst));
+ kfree(inst);
+}
+
+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;
+
+ 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);
+
+ /* Require a keyed message digest */
+ if (!salg->setkey)
+ return -EOPNOTSUPP;
+
+ ds = salg->digestsize;
+ /* Hashes with no digest size are not allowed for KDFs. */
+ if (!ds || WARN_ON(ds > CRYPTO_KDF_MAX_DIGESTSIZE))
+ return -EOPNOTSUPP;
+
+ alg = &salg->base;
+ if (WARN_ON(CRYPTO_KDF_MAX_ALIGNMASK < alg->cra_alignmask))
+ return -EOPNOTSUPP;
+
+ 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 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 = sizeof(struct crypto_kdf_ctx);
+
+ inst->free = crypto_kdf_free;
+
+ err = rng_register_instance(tmpl, inst);
+
+ if (err) {
+ crypto_drop_spawn(rng_instance_ctx(inst));
+free_inst:
+ kfree(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_generate);
+}
+
+static struct crypto_template crypto_kdf_ctr_tmpl = {
+ .name = "kdf_ctr",
+ .create = crypto_kdf_ctr_create,
+ .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_generate);
+}
+
+static struct crypto_template crypto_kdf_fb_tmpl = {
+ .name = "kdf_fb",
+ .create = crypto_kdf_fb_create,
+ .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_generate);
+}
+
+static struct crypto_template crypto_kdf_dpi_tmpl = {
+ .name = "kdf_dpi",
+ .create = crypto_kdf_dpi_create,
+ .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("GPL v2");
+MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
+MODULE_DESCRIPTION("Key Derivation Function conformant to SP800-108");
+MODULE_ALIAS_CRYPTO("kdf_ctr");
+MODULE_ALIAS_CRYPTO("kdf_fb");
+MODULE_ALIAS_CRYPTO("kdf_dpi");
--
2.20.1