crypto: kdf - add SP800-108 counter key derivation function

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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 61 insertions, 0 deletions

diff --git a/include/crypto/kdf_sp800108.h b/include/crypto/kdf_sp800108.h
new file mode 100644
index 000000000000..b7b20a778fb7
--- /dev/null
+++ b/include/crypto/kdf_sp800108.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Copyright (C) 2021, 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 */