diff mbox series

[1/8] crypto,fs: Separate out hkdf_extract() and hkdf_expand()

Message ID 20240718150658.99580-2-hare@kernel.org (mailing list archive)
State Superseded
Delegated to: Herbert Xu
Headers show
Series [1/8] crypto,fs: Separate out hkdf_extract() and hkdf_expand() | expand

Commit Message

Hannes Reinecke July 18, 2024, 3:06 p.m. UTC
Separate out the HKDF functions into a separate file to make them
available to other callers.

Cc: Eric Biggers <ebiggers@kernel.org>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Hannes Reinecke <hare@kernel.org>
---
 crypto/Makefile       |   1 +
 crypto/hkdf.c         | 112 ++++++++++++++++++++++++++++++++++++++++++
 fs/crypto/hkdf.c      |  68 ++++---------------------
 include/crypto/hkdf.h |  18 +++++++
 4 files changed, 140 insertions(+), 59 deletions(-)
 create mode 100644 crypto/hkdf.c
 create mode 100644 include/crypto/hkdf.h

Comments

Eric Biggers July 18, 2024, 11:14 p.m. UTC | #1
On Thu, Jul 18, 2024 at 05:06:51PM +0200, Hannes Reinecke wrote:
> Separate out the HKDF functions into a separate file to make them
> available to other callers.
> 
> Cc: Eric Biggers <ebiggers@kernel.org>
> Cc: linux-crypto@vger.kernel.org
> Signed-off-by: Hannes Reinecke <hare@kernel.org>
> ---
>  crypto/Makefile       |   1 +
>  crypto/hkdf.c         | 112 ++++++++++++++++++++++++++++++++++++++++++
>  fs/crypto/hkdf.c      |  68 ++++---------------------
>  include/crypto/hkdf.h |  18 +++++++
>  4 files changed, 140 insertions(+), 59 deletions(-)
>  create mode 100644 crypto/hkdf.c
>  create mode 100644 include/crypto/hkdf.h

I was only sent patch 1, so this is unreviewable as there is no context.

- Eric
Hannes Reinecke July 19, 2024, 6:13 a.m. UTC | #2
On 7/19/24 01:14, Eric Biggers wrote:
> On Thu, Jul 18, 2024 at 05:06:51PM +0200, Hannes Reinecke wrote:
>> Separate out the HKDF functions into a separate file to make them
>> available to other callers.
>>
>> Cc: Eric Biggers <ebiggers@kernel.org>
>> Cc: linux-crypto@vger.kernel.org
>> Signed-off-by: Hannes Reinecke <hare@kernel.org>
>> ---
>>   crypto/Makefile       |   1 +
>>   crypto/hkdf.c         | 112 ++++++++++++++++++++++++++++++++++++++++++
>>   fs/crypto/hkdf.c      |  68 ++++---------------------
>>   include/crypto/hkdf.h |  18 +++++++
>>   4 files changed, 140 insertions(+), 59 deletions(-)
>>   create mode 100644 crypto/hkdf.c
>>   create mode 100644 include/crypto/hkdf.h
> 
> I was only sent patch 1, so this is unreviewable as there is no context.
> 
Sorry. Will include you with the full patchset for the next round.
The remainder of the patch series is just calling into the just exported
functions to derive TLS PSK keys, wasn't sure if you'd be interested in
that.

Cheers,

Hannes
diff mbox series

Patch

diff --git a/crypto/Makefile b/crypto/Makefile
index edbbaa3ffef5..b77fc360f0ff 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -29,6 +29,7 @@  obj-$(CONFIG_CRYPTO_ECHAINIV) += echainiv.o
 
 crypto_hash-y += ahash.o
 crypto_hash-y += shash.o
+crypto_hash-y += hkdf.o
 obj-$(CONFIG_CRYPTO_HASH2) += crypto_hash.o
 
 obj-$(CONFIG_CRYPTO_AKCIPHER2) += akcipher.o
diff --git a/crypto/hkdf.c b/crypto/hkdf.c
new file mode 100644
index 000000000000..22e343851c0b
--- /dev/null
+++ b/crypto/hkdf.c
@@ -0,0 +1,112 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implementation of HKDF ("HMAC-based Extract-and-Expand Key Derivation
+ * Function"), aka RFC 5869.  See also the original paper (Krawczyk 2010):
+ * "Cryptographic Extraction and Key Derivation: The HKDF Scheme".
+ *
+ * This is used to derive keys from the fscrypt master keys.
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include <crypto/hash.h>
+#include <crypto/sha2.h>
+#include <crypto/hkdf.h>
+
+/*
+ * HKDF consists of two steps:
+ *
+ * 1. HKDF-Extract: extract a pseudorandom key of length HKDF_HASHLEN bytes from
+ *    the input keying material and optional salt.
+ * 2. HKDF-Expand: expand the pseudorandom key into output keying material of
+ *    any length, parameterized by an application-specific info string.
+ *
+ */
+
+/* HKDF-Extract (RFC 5869 section 2.2), unsalted */
+int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm,
+		 unsigned int ikmlen, u8 *prk)
+{
+	unsigned int prklen = crypto_shash_digestsize(hmac_tfm);
+	u8 *default_salt;
+	int err;
+
+	default_salt = kzalloc(prklen, GFP_KERNEL);
+	if (!default_salt)
+		return -ENOMEM;
+	err = crypto_shash_setkey(hmac_tfm, default_salt, prklen);
+	if (!err)
+		err = crypto_shash_tfm_digest(hmac_tfm, ikm, ikmlen, prk);
+
+	kfree(default_salt);
+	return err;
+}
+EXPORT_SYMBOL_GPL(hkdf_extract);
+
+/*
+ * HKDF-Expand (RFC 5869 section 2.3).
+ * This expands the pseudorandom key, which was already keyed into @hmac_tfm,
+ * into @okmlen bytes of output keying material parameterized by the
+ * application-specific @info of length @infolen bytes.
+ * This is thread-safe and may be called by multiple threads in parallel.
+ */
+int hkdf_expand(struct crypto_shash *hmac_tfm,
+		const u8 *info, unsigned int infolen,
+		u8 *okm, unsigned int okmlen)
+{
+	SHASH_DESC_ON_STACK(desc, hmac_tfm);
+	unsigned int i, hashlen = crypto_shash_digestsize(hmac_tfm);
+	int err;
+	const u8 *prev = NULL;
+	u8 counter = 1;
+	u8 *tmp;
+
+	if (WARN_ON(okmlen > 255 * hashlen))
+		return -EINVAL;
+
+	tmp = kzalloc(hashlen, GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
+	desc->tfm = hmac_tfm;
+
+	for (i = 0; i < okmlen; i += hashlen) {
+
+		err = crypto_shash_init(desc);
+		if (err)
+			goto out;
+
+		if (prev) {
+			err = crypto_shash_update(desc, prev, hashlen);
+			if (err)
+				goto out;
+		}
+
+		err = crypto_shash_update(desc, info, infolen);
+		if (err)
+			goto out;
+
+		BUILD_BUG_ON(sizeof(counter) != 1);
+		if (okmlen - i < hashlen) {
+			err = crypto_shash_finup(desc, &counter, 1, tmp);
+			if (err)
+				goto out;
+			memcpy(&okm[i], tmp, okmlen - i);
+			memzero_explicit(tmp, sizeof(tmp));
+		} else {
+			err = crypto_shash_finup(desc, &counter, 1, &okm[i]);
+			if (err)
+				goto out;
+		}
+		counter++;
+		prev = &okm[i];
+	}
+	err = 0;
+out:
+	if (unlikely(err))
+		memzero_explicit(okm, okmlen); /* so caller doesn't need to */
+	shash_desc_zero(desc);
+	kfree(tmp);
+	return err;
+}
+EXPORT_SYMBOL_GPL(hkdf_expand);
diff --git a/fs/crypto/hkdf.c b/fs/crypto/hkdf.c
index 5a384dad2c72..9c2f9aca9412 100644
--- a/fs/crypto/hkdf.c
+++ b/fs/crypto/hkdf.c
@@ -11,6 +11,7 @@ 
 
 #include <crypto/hash.h>
 #include <crypto/sha2.h>
+#include <crypto/hkdf.h>
 
 #include "fscrypt_private.h"
 
@@ -44,20 +45,6 @@ 
  * there's no way to persist a random salt per master key from kernel mode.
  */
 
-/* HKDF-Extract (RFC 5869 section 2.2), unsalted */
-static int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm,
-			unsigned int ikmlen, u8 prk[HKDF_HASHLEN])
-{
-	static const u8 default_salt[HKDF_HASHLEN];
-	int err;
-
-	err = crypto_shash_setkey(hmac_tfm, default_salt, HKDF_HASHLEN);
-	if (err)
-		return err;
-
-	return crypto_shash_tfm_digest(hmac_tfm, ikm, ikmlen, prk);
-}
-
 /*
  * Compute HKDF-Extract using the given master key as the input keying material,
  * and prepare an HMAC transform object keyed by the resulting pseudorandom key.
@@ -118,61 +105,24 @@  int fscrypt_hkdf_expand(const struct fscrypt_hkdf *hkdf, u8 context,
 			u8 *okm, unsigned int okmlen)
 {
 	SHASH_DESC_ON_STACK(desc, hkdf->hmac_tfm);
-	u8 prefix[9];
-	unsigned int i;
+	u8 *prefix;
 	int err;
-	const u8 *prev = NULL;
-	u8 counter = 1;
-	u8 tmp[HKDF_HASHLEN];
 
 	if (WARN_ON_ONCE(okmlen > 255 * HKDF_HASHLEN))
 		return -EINVAL;
 
+	prefix = kzalloc(okmlen + 9, GFP_KERNEL);
+	if (!prefix)
+		return -ENOMEM;
 	desc->tfm = hkdf->hmac_tfm;
 
 	memcpy(prefix, "fscrypt\0", 8);
 	prefix[8] = context;
+	memcpy(prefix + 9, info, infolen);
 
-	for (i = 0; i < okmlen; i += HKDF_HASHLEN) {
-
-		err = crypto_shash_init(desc);
-		if (err)
-			goto out;
-
-		if (prev) {
-			err = crypto_shash_update(desc, prev, HKDF_HASHLEN);
-			if (err)
-				goto out;
-		}
-
-		err = crypto_shash_update(desc, prefix, sizeof(prefix));
-		if (err)
-			goto out;
-
-		err = crypto_shash_update(desc, info, infolen);
-		if (err)
-			goto out;
-
-		BUILD_BUG_ON(sizeof(counter) != 1);
-		if (okmlen - i < HKDF_HASHLEN) {
-			err = crypto_shash_finup(desc, &counter, 1, tmp);
-			if (err)
-				goto out;
-			memcpy(&okm[i], tmp, okmlen - i);
-			memzero_explicit(tmp, sizeof(tmp));
-		} else {
-			err = crypto_shash_finup(desc, &counter, 1, &okm[i]);
-			if (err)
-				goto out;
-		}
-		counter++;
-		prev = &okm[i];
-	}
-	err = 0;
-out:
-	if (unlikely(err))
-		memzero_explicit(okm, okmlen); /* so caller doesn't need to */
-	shash_desc_zero(desc);
+	err = hkdf_expand(hkdf->hmac_tfm, prefix, infolen + 8,
+			  okm, okmlen);
+	kfree(prefix);
 	return err;
 }
 
diff --git a/include/crypto/hkdf.h b/include/crypto/hkdf.h
new file mode 100644
index 000000000000..bf06c080d7ed
--- /dev/null
+++ b/include/crypto/hkdf.h
@@ -0,0 +1,18 @@ 
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * HKDF: HMAC-based Key Derivation Function (HKDF), RFC 5869
+ *
+ * Extracted from fs/crypto/hkdf.c, which has
+ * Copyright 2019 Google LLC
+ */
+
+#ifndef _CRYPTO_HKDF_H
+#define _CRYPTO_HKDF_H
+
+int hkdf_extract(struct crypto_shash *hmac_tfm, const u8 *ikm,
+		 unsigned int ikmlen, u8 *prk);
+int hkdf_expand(struct crypto_shash *hmac_tfm,
+		const u8 *info, unsigned int infolen,
+		u8 *okm, unsigned int okmlen);
+
+#endif