[PATCH net 10/24] crypto/krb5: Implement the Kerberos5 rfc3961 key derivation

David Howells
2025-02-03T14:25:02Z

Implement the simplified crypto profile for Kerberos 5 rfc3961 with the
pseudo-random function, PRF(), from section 5.3 and the key derivation
function, DK() from section 5.1.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Herbert Xu <herbert@gondor.apana.org.au>
cc: "David S. Miller" <davem@davemloft.net>
cc: Chuck Lever <chuck.lever@oracle.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: linux-nfs@vger.kernel.org
cc: linux-crypto@vger.kernel.org
cc: netdev@vger.kernel.org
---
crypto/krb5/Makefile | 3 +-
crypto/krb5/internal.h | 6 +
crypto/krb5/rfc3961_simplified.c | 407 +++++++++++++++++++++++++++++++
3 files changed, 415 insertions(+), 1 deletion(-)
create mode 100644 crypto/krb5/rfc3961_simplified.c

diff --git a/crypto/krb5/Makefile b/crypto/krb5/Makefile
index 8c2050af8fed..8dad8e3bf086 100644
--- a/crypto/krb5/Makefile
+++ b/crypto/krb5/Makefile
@@ -5,6 +5,7 @@

krb5-y += \
krb5_kdf.o \
- krb5_api.o
+ krb5_api.o \
+ rfc3961_simplified.o

obj-$(CONFIG_CRYPTO_KRB5) += krb5.o
diff --git a/crypto/krb5/internal.h b/crypto/krb5/internal.h
index 50abda5169c7..7d60977dc0c5 100644
--- a/crypto/krb5/internal.h
+++ b/crypto/krb5/internal.h
@@ -5,6 +5,7 @@
* Written by David Howells (dhowells@redhat.com)
*/

+#include <linux/scatterlist.h>
#include <crypto/krb5.h>

/*
@@ -130,3 +131,8 @@ int krb5_derive_Ke(const struct krb5_enctype *krb5, const struct krb5_buffer *TK
u32 usage, struct krb5_buffer *key, gfp_t gfp);
int krb5_derive_Ki(const struct krb5_enctype *krb5, const struct krb5_buffer *TK,
u32 usage, struct krb5_buffer *key, gfp_t gfp);
+
+/*
+ * rfc3961_simplified.c
+ */
+extern const struct krb5_crypto_profile rfc3961_simplified_profile;
diff --git a/crypto/krb5/rfc3961_simplified.c b/crypto/krb5/rfc3961_simplified.c
new file mode 100644
index 000000000000..75eafba059c7
--- /dev/null
+++ b/crypto/krb5/rfc3961_simplified.c
@@ -0,0 +1,407 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/* rfc3961 Kerberos 5 simplified crypto profile.
+ *
+ * Parts borrowed from net/sunrpc/auth_gss/.
+ */
+/*
+ * COPYRIGHT (c) 2008
+ * The Regents of the University of Michigan
+ * ALL RIGHTS RESERVED
+ *
+ * Permission is granted to use, copy, create derivative works
+ * and redistribute this software and such derivative works
+ * for any purpose, so long as the name of The University of
+ * Michigan is not used in any advertising or publicity
+ * pertaining to the use of distribution of this software
+ * without specific, written prior authorization. If the
+ * above copyright notice or any other identification of the
+ * University of Michigan is included in any copy of any
+ * portion of this software, then the disclaimer below must
+ * also be included.
+ *
+ * THIS SOFTWARE IS PROVIDED AS IS, WITHOUT REPRESENTATION
+ * FROM THE UNIVERSITY OF MICHIGAN AS TO ITS FITNESS FOR ANY
+ * PURPOSE, AND WITHOUT WARRANTY BY THE UNIVERSITY OF
+ * MICHIGAN OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING
+ * WITHOUT LIMITATION THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
+ * REGENTS OF THE UNIVERSITY OF MICHIGAN SHALL NOT BE LIABLE
+ * FOR ANY DAMAGES, INCLUDING SPECIAL, INDIRECT, INCIDENTAL, OR
+ * CONSEQUENTIAL DAMAGES, WITH RESPECT TO ANY CLAIM ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OF THE SOFTWARE, EVEN
+ * IF IT HAS BEEN OR IS HEREAFTER ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGES.
+ */
+
+/*
+ * Copyright (C) 1998 by the FundsXpress, INC.
+ *
+ * All rights reserved.
+ *
+ * Export of this software from the United States of America may require
+ * a specific license from the United States Government. It is the
+ * responsibility of any person or organization contemplating export to
+ * obtain such a license before exporting.
+ *
+ * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
+ * distribute this software and its documentation for any purpose and
+ * without fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright notice and
+ * this permission notice appear in supporting documentation, and that
+ * the name of FundsXpress. not be used in advertising or publicity pertaining
+ * to distribution of the software without specific, written prior
+ * permission. FundsXpress makes no representations about the suitability of
+ * this software for any purpose. It is provided "as is" without express
+ * or implied warranty.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+/*
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/slab.h>
+#include <linux/lcm.h>
+#include <crypto/skcipher.h>
+#include <crypto/hash.h>
+#include "internal.h"
+
+/* Maximum blocksize for the supported crypto algorithms */
+#define KRB5_MAX_BLOCKSIZE (16)
+
+static int rfc3961_do_encrypt(struct crypto_sync_skcipher *tfm, void *iv,
+ const struct krb5_buffer *in, struct krb5_buffer *out)
+{
+ struct scatterlist sg[1];
+ u8 local_iv[KRB5_MAX_BLOCKSIZE] __aligned(KRB5_MAX_BLOCKSIZE) = {0};
+ SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);
+ int ret;
+
+ if (WARN_ON(in->len != out->len))
+ return -EINVAL;
+ if (out->len % crypto_sync_skcipher_blocksize(tfm) != 0)
+ return -EINVAL;
+
+ if (crypto_sync_skcipher_ivsize(tfm) > KRB5_MAX_BLOCKSIZE)
+ return -EINVAL;
+
+ if (iv)
+ memcpy(local_iv, iv, crypto_sync_skcipher_ivsize(tfm));
+
+ memcpy(out->data, in->data, out->len);
+ sg_init_one(sg, out->data, out->len);
+
+ skcipher_request_set_sync_tfm(req, tfm);
+ skcipher_request_set_callback(req, 0, NULL, NULL);
+ skcipher_request_set_crypt(req, sg, sg, out->len, local_iv);
+
+ ret = crypto_skcipher_encrypt(req);
+ skcipher_request_zero(req);
+ return ret;
+}
+
+/*
+ * Calculate an unkeyed basic hash.
+ */
+static int rfc3961_calc_H(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *data,
+ struct krb5_buffer *digest,
+ gfp_t gfp)
+{
+ struct crypto_shash *tfm;
+ struct shash_desc *desc;
+ size_t desc_size;
+ int ret = -ENOMEM;
+
+ tfm = crypto_alloc_shash(krb5->hash_name, 0, 0);
+ if (IS_ERR(tfm))
+ return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
+
+ desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+
+ desc = kzalloc(desc_size, gfp);
+ if (!desc)
+ goto error_tfm;
+
+ digest->len = crypto_shash_digestsize(tfm);
+ digest->data = kzalloc(digest->len, gfp);
+ if (!digest->data)
+ goto error_desc;
+
+ desc->tfm = tfm;
+ ret = crypto_shash_init(desc);
+ if (ret < 0)
+ goto error_digest;
+
+ ret = crypto_shash_finup(desc, data->data, data->len, digest->data);
+ if (ret < 0)
+ goto error_digest;
+
+ goto error_desc;
+
+error_digest:
+ kfree_sensitive(digest->data);
+error_desc:
+ kfree_sensitive(desc);
+error_tfm:
+ crypto_free_shash(tfm);
+ return ret;
+}
+
+/*
+ * This is the n-fold function as described in rfc3961, sec 5.1
+ * Taken from MIT Kerberos and modified.
+ */
+static void rfc3961_nfold(const struct krb5_buffer *source, struct krb5_buffer *result)
+{
+ const u8 *in = source->data;
+ u8 *out = result->data;
+ unsigned long ulcm;
+ unsigned int inbits, outbits;
+ int byte, i, msbit;
+
+ /* the code below is more readable if I make these bytes instead of bits */
+ inbits = source->len;
+ outbits = result->len;
+
+ /* first compute lcm(n,k) */
+ ulcm = lcm(inbits, outbits);
+
+ /* now do the real work */
+ memset(out, 0, outbits);
+ byte = 0;
+
+ /* this will end up cycling through k lcm(k,n)/k times, which
+ * is correct.
+ */
+ for (i = ulcm-1; i >= 0; i--) {
+ /* compute the msbit in k which gets added into this byte */
+ msbit = (
+ /* first, start with the msbit in the first,
+ * unrotated byte
+ */
+ ((inbits << 3) - 1) +
+ /* then, for each byte, shift to the right
+ * for each repetition
+ */
+ (((inbits << 3) + 13) * (i/inbits)) +
+ /* last, pick out the correct byte within
+ * that shifted repetition
+ */
+ ((inbits - (i % inbits)) << 3)
+ ) % (inbits << 3);
+
+ /* pull out the byte value itself */
+ byte += (((in[((inbits - 1) - (msbit >> 3)) % inbits] << 8) |
+ (in[((inbits) - (msbit >> 3)) % inbits]))
+ >> ((msbit & 7) + 1)) & 0xff;
+
+ /* do the addition */
+ byte += out[i % outbits];
+ out[i % outbits] = byte & 0xff;
+
+ /* keep around the carry bit, if any */
+ byte >>= 8;
+ }
+
+ /* if there's a carry bit left over, add it back in */
+ if (byte) {
+ for (i = outbits - 1; i >= 0; i--) {
+ /* do the addition */
+ byte += out[i];
+ out[i] = byte & 0xff;
+
+ /* keep around the carry bit, if any */
+ byte >>= 8;
+ }
+ }
+}
+
+/*
+ * Calculate a derived key, DK(Base Key, Well-Known Constant)
+ *
+ * DK(Key, Constant) = random-to-key(DR(Key, Constant))
+ * DR(Key, Constant) = k-truncate(E(Key, Constant, initial-cipher-state))
+ * K1 = E(Key, n-fold(Constant), initial-cipher-state)
+ * K2 = E(Key, K1, initial-cipher-state)
+ * K3 = E(Key, K2, initial-cipher-state)
+ * K4 = ...
+ * DR(Key, Constant) = k-truncate(K1 | K2 | K3 | K4 ...)
+ * [rfc3961 sec 5.1]
+ */
+static int rfc3961_calc_DK(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *inkey,
+ const struct krb5_buffer *in_constant,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ unsigned int blocksize, keybytes, keylength, n;
+ struct krb5_buffer inblock, outblock, rawkey;
+ struct crypto_sync_skcipher *cipher;
+ int ret = -EINVAL;
+
+ blocksize = krb5->block_len;
+ keybytes = krb5->key_bytes;
+ keylength = krb5->key_len;
+
+ if (inkey->len != keylength || result->len != keylength)
+ return -EINVAL;
+ if (!krb5->random_to_key && result->len != keybytes)
+ return -EINVAL;
+
+ cipher = crypto_alloc_sync_skcipher(krb5->derivation_enc, 0, 0);
+ if (IS_ERR(cipher)) {
+ ret = (PTR_ERR(cipher) == -ENOENT) ? -ENOPKG : PTR_ERR(cipher);
+ goto err_return;
+ }
+ ret = crypto_sync_skcipher_setkey(cipher, inkey->data, inkey->len);
+ if (ret < 0)
+ goto err_free_cipher;
+
+ ret = -ENOMEM;
+ inblock.data = kzalloc(blocksize * 2 + keybytes, gfp);
+ if (!inblock.data)
+ goto err_free_cipher;
+
+ inblock.len = blocksize;
+ outblock.data = inblock.data + blocksize;
+ outblock.len = blocksize;
+ rawkey.data = outblock.data + blocksize;
+ rawkey.len = keybytes;
+
+ /* initialize the input block */
+
+ if (in_constant->len == inblock.len)
+ memcpy(inblock.data, in_constant->data, inblock.len);
+ else
+ rfc3961_nfold(in_constant, &inblock);
+
+ /* loop encrypting the blocks until enough key bytes are generated */
+ n = 0;
+ while (n < rawkey.len) {
+ rfc3961_do_encrypt(cipher, NULL, &inblock, &outblock);
+
+ if (keybytes - n <= outblock.len) {
+ memcpy(rawkey.data + n, outblock.data, keybytes - n);
+ break;
+ }
+
+ memcpy(rawkey.data + n, outblock.data, outblock.len);
+ memcpy(inblock.data, outblock.data, outblock.len);
+ n += outblock.len;
+ }
+
+ /* postprocess the key */
+ if (!krb5->random_to_key) {
+ /* Identity random-to-key function. */
+ memcpy(result->data, rawkey.data, rawkey.len);
+ ret = 0;
+ } else {
+ ret = krb5->random_to_key(krb5, &rawkey, result);
+ }
+
+ kfree_sensitive(inblock.data);
+err_free_cipher:
+ crypto_free_sync_skcipher(cipher);
+err_return:
+ return ret;
+}
+
+/*
+ * Calculate single encryption, E()
+ *
+ * E(Key, octets)
+ */
+static int rfc3961_calc_E(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *key,
+ const struct krb5_buffer *in_data,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ struct crypto_sync_skcipher *cipher;
+ int ret;
+
+ cipher = crypto_alloc_sync_skcipher(krb5->derivation_enc, 0, 0);
+ if (IS_ERR(cipher)) {
+ ret = (PTR_ERR(cipher) == -ENOENT) ? -ENOPKG : PTR_ERR(cipher);
+ goto err;
+ }
+
+ ret = crypto_sync_skcipher_setkey(cipher, key->data, key->len);
+ if (ret < 0)
+ goto err_free;
+
+ ret = rfc3961_do_encrypt(cipher, NULL, in_data, result);
+
+err_free:
+ crypto_free_sync_skcipher(cipher);
+err:
+ return ret;
+}
+
+/*
+ * Calculate the pseudo-random function, PRF().
+ *
+ * tmp1 = H(octet-string)
+ * tmp2 = truncate tmp1 to multiple of m
+ * PRF = E(DK(protocol-key, prfconstant), tmp2, initial-cipher-state)
+ *
+ * The "prfconstant" used in the PRF operation is the three-octet string
+ * "prf".
+ * [rfc3961 sec 5.3]
+ */
+static int rfc3961_calc_PRF(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *protocol_key,
+ const struct krb5_buffer *octet_string,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ static const struct krb5_buffer prfconstant = { 3, "prf" };
+ struct krb5_buffer derived_key;
+ struct krb5_buffer tmp1, tmp2;
+ unsigned int m = krb5->block_len;
+ void *buffer;
+ int ret;
+
+ if (result->len != krb5->prf_len)
+ return -EINVAL;
+
+ tmp1.len = krb5->hash_len;
+ derived_key.len = krb5->key_bytes;
+ buffer = kzalloc(round16(tmp1.len) + round16(derived_key.len), gfp);
+ if (!buffer)
+ return -ENOMEM;
+
+ tmp1.data = buffer;
+ derived_key.data = buffer + round16(tmp1.len);
+
+ ret = rfc3961_calc_H(krb5, octet_string, &tmp1, gfp);
+ if (ret < 0)
+ goto err;
+
+ tmp2.len = tmp1.len & ~(m - 1);
+ tmp2.data = tmp1.data;
+
+ ret = rfc3961_calc_DK(krb5, protocol_key, &prfconstant, &derived_key, gfp);
+ if (ret < 0)
+ goto err;
+
+ ret = rfc3961_calc_E(krb5, &derived_key, &tmp2, result, gfp);
+
+err:
+ kfree_sensitive(buffer);
+ return ret;
+}
+
+const struct krb5_crypto_profile rfc3961_simplified_profile = {
+ .calc_PRF = rfc3961_calc_PRF,
+ .calc_Kc = rfc3961_calc_DK,
+ .calc_Ke = rfc3961_calc_DK,
+ .calc_Ki = rfc3961_calc_DK,
+};