diff options
Diffstat (limited to 'fs/crypto/hkdf.c')
| -rw-r--r-- | fs/crypto/hkdf.c | 85 |
1 files changed, 15 insertions, 70 deletions
diff --git a/fs/crypto/hkdf.c b/fs/crypto/hkdf.c index 5a384dad2c72..855a0f4b7318 100644 --- a/fs/crypto/hkdf.c +++ b/fs/crypto/hkdf.c @@ -1,9 +1,5 @@ // 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 @@ -11,6 +7,7 @@ #include <crypto/hash.h> #include <crypto/sha2.h> +#include <crypto/hkdf.h> #include "fscrypt_private.h" @@ -44,20 +41,6 @@ * 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. @@ -69,6 +52,7 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key, unsigned int master_key_size) { struct crypto_shash *hmac_tfm; + static const u8 default_salt[HKDF_HASHLEN]; u8 prk[HKDF_HASHLEN]; int err; @@ -84,7 +68,8 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key, goto err_free_tfm; } - err = hkdf_extract(hmac_tfm, master_key, master_key_size, prk); + err = hkdf_extract(hmac_tfm, master_key, master_key_size, + default_salt, HKDF_HASHLEN, prk); if (err) goto err_free_tfm; @@ -118,61 +103,21 @@ 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 *full_info; int err; - const u8 *prev = NULL; - u8 counter = 1; - u8 tmp[HKDF_HASHLEN]; - - if (WARN_ON_ONCE(okmlen > 255 * HKDF_HASHLEN)) - return -EINVAL; + full_info = kzalloc(infolen + 9, GFP_KERNEL); + if (!full_info) + return -ENOMEM; desc->tfm = hkdf->hmac_tfm; - memcpy(prefix, "fscrypt\0", 8); - prefix[8] = context; - - 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); + memcpy(full_info, "fscrypt\0", 8); + full_info[8] = context; + memcpy(full_info + 9, info, infolen); + + err = hkdf_expand(hkdf->hmac_tfm, full_info, infolen + 9, + okm, okmlen); + kfree_sensitive(full_info); return err; } |