[PATCH v2 2/7] crypto: add SP800-108 counter key derivation function

Stephan Müller
2021-01-24T14:10:19Z

SP800-108 defines three KDFs - this patch provides the counter KDF
implementation.

The KDF is implemented as a service function where the caller has to
maintain the hash / HMAC state. Apart from this hash/HMAC state, no
additional state is required to be maintained by either the caller or
the KDF implementation.

The key for the KDF is set with the crypto_kdf108_setkey function which
is intended to be invoked before the caller requests a key derivation
operation via crypto_kdf108_ctr_generate.

SP800-108 allows the use of either a HMAC or a hash as crypto primitive
for the KDF. When a HMAC primtive is intended to be used,
crypto_kdf108_setkey must be used to set the HMAC key. Otherwise, for a
hash crypto primitve crypto_kdf108_ctr_generate can be used immediately
after allocating the hash handle.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
crypto/Kconfig | 7 ++
crypto/Makefile | 5 ++
crypto/kdf_sp800108.c | 149 ++++++++++++++++++++++++++++++++++
include/crypto/kdf_sp800108.h | 61 ++++++++++++++
4 files changed, 222 insertions(+)
create mode 100644 crypto/kdf_sp800108.c
create mode 100644 include/crypto/kdf_sp800108.h

diff --git a/crypto/Kconfig b/crypto/Kconfig
index a367fcfeb5d4..9f375c2350f5 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1862,6 +1862,13 @@ config CRYPTO_JITTERENTROPY
random numbers. This Jitterentropy RNG registers with
the kernel crypto API and can be used by any caller.

+config CRYPTO_KDF800108_CTR
+ tristate "Counter KDF (SP800-108)"
+ select CRYPTO_HASH
+ help
+ Enable the key derivation function in counter mode compliant to
+ SP800-108.
+
config CRYPTO_USER_API
tristate

diff --git a/crypto/Makefile b/crypto/Makefile
index b279483fba50..46845a70850d 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -197,3 +197,8 @@ obj-$(CONFIG_ASYMMETRIC_KEY_TYPE) += asymmetric_keys/
obj-$(CONFIG_CRYPTO_HASH_INFO) += hash_info.o
crypto_simd-y := simd.o
obj-$(CONFIG_CRYPTO_SIMD) += crypto_simd.o
+
+#
+# Key derivation function
+#
+obj-$(CONFIG_CRYPTO_KDF800108_CTR) += kdf_sp800108.o
diff --git a/crypto/kdf_sp800108.c b/crypto/kdf_sp800108.c
new file mode 100644
index 000000000000..84b45e0cadf5
--- /dev/null
+++ b/crypto/kdf_sp800108.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * SP800-108 Key-derivation function
+ *
+ * Copyright (C) 2020, Stephan Mueller <smueller@chronox.de>
+ */
+
+#include <linux/module.h>
+#include <crypto/kdf_sp800108.h>
+#include <crypto/internal/kdf_selftest.h>
+
+/*
+ * SP800-108 CTR KDF implementation
+ */
+int crypto_kdf108_ctr_generate(struct crypto_shash *kmd,
+ const struct kvec *info, unsigned int info_nvec,
+ u8 *dst, unsigned int dlen)
+{
+ SHASH_DESC_ON_STACK(desc, kmd);
+ __be32 counter = cpu_to_be32(1);
+ const unsigned int h = crypto_shash_digestsize(kmd), dlen_orig = dlen;
+ unsigned int i;
+ int err = 0;
+ u8 *dst_orig = dst;
+
+ desc->tfm = 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;
+
+ for (i = 0; i < info_nvec; i++) {
+ err = crypto_shash_update(desc, info[i].iov_base,
+ info[i].iov_len);
+ if (err)
+ goto out;
+ }
+
+ if (dlen < h) {
+ u8 tmpbuffer[HASH_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_orig);
+ shash_desc_zero(desc);
+ return err;
+}
+EXPORT_SYMBOL(crypto_kdf108_ctr_generate);
+
+/*
+ * The seeding of the KDF
+ */
+int crypto_kdf108_setkey(struct crypto_shash *kmd,
+ const u8 *key, size_t keylen,
+ const u8 *ikm, size_t ikmlen)
+{
+ unsigned int ds = crypto_shash_digestsize(kmd);
+
+ /* SP800-108 does not support IKM */
+ if (ikm || ikmlen)
+ return -EINVAL;
+
+ /* Check according to SP800-108 section 7.2 */
+ if (ds > keylen)
+ 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(kmd, key, keylen);
+}
+EXPORT_SYMBOL(crypto_kdf108_setkey);
+
+/*
+ * Test vector obtained from
+ * http://csrc.nist.gov/groups/STM/cavp/documents/KBKDF800-108/CounterMode.zip
+ */
+static const struct kdf_testvec kdf_ctr_hmac_sha256_tv_template[] = {
+ {
+ .key = "\xdd\x1d\x91\xb7\xd9\x0b\x2b\xd3"
+ "\x13\x85\x33\xce\x92\xb2\x72\xfb"
+ "\xf8\xa3\x69\x31\x6a\xef\xe2\x42"
+ "\xe6\x59\xcc\x0a\xe2\x38\xaf\xe0",
+ .keylen = 32,
+ .ikm = NULL,
+ .ikmlen = 0,
+ .info = {
+ .iov_base = "\x01\x32\x2b\x96\xb3\x0a\xcd\x19"
+ "\x79\x79\x44\x4e\x46\x8e\x1c\x5c"
+ "\x68\x59\xbf\x1b\x1c\xf9\x51\xb7"
+ "\xe7\x25\x30\x3e\x23\x7e\x46\xb8"
+ "\x64\xa1\x45\xfa\xb2\x5e\x51\x7b"
+ "\x08\xf8\x68\x3d\x03\x15\xbb\x29"
+ "\x11\xd8\x0a\x0e\x8a\xba\x17\xf3"
+ "\xb4\x13\xfa\xac",
+ .iov_len = 60
+ },
+ .expected = "\x10\x62\x13\x42\xbf\xb0\xfd\x40"
+ "\x04\x6c\x0e\x29\xf2\xcf\xdb\xf0",
+ .expectedlen = 16
+ }
+};
+
+static int __init crypto_kdf108_init(void)
+{
+ int ret = kdf_test(&kdf_ctr_hmac_sha256_tv_template[0], "hmac(sha256)",
+ crypto_kdf108_setkey, crypto_kdf108_ctr_generate);
+
+ if (ret)
+ pr_warn("alg: self-tests for CTR-KDF (hmac(sha256)) failed (rc=%d)\n",
+ ret);
+ else
+ pr_info("alg: self-tests for CTR-KDF (hmac(sha256)) passed\n");
+
+ return ret;
+}
+
+static void __exit crypto_kdf108_exit(void) { }
+
+module_init(crypto_kdf108_init);
+module_exit(crypto_kdf108_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Stephan Mueller <smueller@chronox.de>");
+MODULE_DESCRIPTION("Key Derivation Function conformant to SP800-108");
diff --git a/include/crypto/kdf_sp800108.h b/include/crypto/kdf_sp800108.h
new file mode 100644
index 000000000000..fdc360bd9cd6
--- /dev/null
+++ b/include/crypto/kdf_sp800108.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2020, Stephan Mueller <smueller@chronox.de>
+ */
+
+#ifndef _CRYPTO_KDF108_H
+#define _CRYPTO_KDF108_H
+
+#include <crypto/hash.h>
+#include <linux/uio.h>
+
+/**
+ * Counter KDF generate operation according to SP800-108 section 5.1
+ * as well as SP800-56A section 5.8.1 (Single-step KDF).
+ *
+ * @kmd Keyed message digest whose key was set with crypto_kdf108_setkey or
+ * unkeyed message digest
+ * @info optional context and application specific information - this may be
+ * NULL
+ * @info_vec number of optional context/application specific information entries
+ * @dst destination buffer that the caller already allocated
+ * @dlen length of the destination buffer - the KDF derives that amount of
+ * bytes.
+ *
+ * To comply with SP800-108, the caller must provide Label || 0x00 || Context
+ * in the info parameter.
+ *
+ * @return 0 on success, < 0 on error
+ */
+int crypto_kdf108_ctr_generate(struct crypto_shash *kmd,
+ const struct kvec *info, unsigned int info_nvec,
+ u8 *dst, unsigned int dlen);
+
+/**
+ * Counter KDF setkey operation
+ *
+ * @kmd Keyed message digest allocated by the caller. The key should not have
+ * been set.
+ * @key Seed key to be used to initialize the keyed message digest context.
+ * @keylen This length of the key buffer.
+ * @ikm The SP800-108 KDF does not support IKM - this parameter must be NULL
+ * @ikmlen This parameter must be 0.
+ *
+ * According to SP800-108 section 7.2, the seed key must be at least as large as
+ * the message digest size of the used keyed message digest. This limitation
+ * is enforced by the implementation.
+ *
+ * SP800-108 allows the use of either a HMAC or a hash primitive. When
+ * the caller intends to use a hash primitive, the call to
+ * crypto_kdf108_setkey is not required and the key derivation operation can
+ * immediately performed using crypto_kdf108_ctr_generate after allocating
+ * a handle.
+ *
+ * @return 0 on success, < 0 on error
+ */
+int crypto_kdf108_setkey(struct crypto_shash *kmd,
+ const u8 *key, size_t keylen,
+ const u8 *ikm, size_t ikmlen);
+
+#endif /* _CRYPTO_KDF108_H */
--
2.26.2