1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Kerberos key derivation.
3 *
4 * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/export.h>
11#include <linux/slab.h>
12#include <crypto/skcipher.h>
13#include <crypto/hash.h>
14#include "internal.h"
15
16/**
17 * crypto_krb5_calc_PRFplus - Calculate PRF+ [RFC4402]
18 * @krb5: The encryption type to use
19 * @K: The protocol key for the pseudo-random function
20 * @L: The length of the output
21 * @S: The input octet string
22 * @result: Result buffer, sized to krb5->prf_len
23 * @gfp: Allocation restrictions
24 *
25 * Calculate the kerberos pseudo-random function, PRF+() by the following
26 * method:
27 *
28 * PRF+(K, L, S) = truncate(L, T1 || T2 || .. || Tn)
29 * Tn = PRF(K, n || S)
30 * [rfc4402 sec 2]
31 */
32int crypto_krb5_calc_PRFplus(const struct krb5_enctype *krb5,
33 const struct krb5_buffer *K,
34 unsigned int L,
35 const struct krb5_buffer *S,
36 struct krb5_buffer *result,
37 gfp_t gfp)
38{
39 struct krb5_buffer T_series, Tn, n_S;
40 void *buffer;
41 int ret, n = 1;
42
43 Tn.len = krb5->prf_len;
44 T_series.len = 0;
45 n_S.len = 4 + S->len;
46
47 buffer = kzalloc(round16(L + Tn.len) + round16(n_S.len), gfp);
48 if (!buffer)
49 return -ENOMEM;
50
51 T_series.data = buffer;
52 n_S.data = buffer + round16(L + Tn.len);
53 memcpy(n_S.data + 4, S->data, S->len);
54
55 while (T_series.len < L) {
56 *(__be32 *)(n_S.data) = htonl(n);
57 Tn.data = T_series.data + Tn.len * (n - 1);
58 ret = krb5->profile->calc_PRF(krb5, K, &n_S, &Tn, gfp);
59 if (ret < 0)
60 goto err;
61 T_series.len += Tn.len;
62 n++;
63 }
64
65 /* Truncate to L */
66 memcpy(result->data, T_series.data, L);
67 ret = 0;
68
69err:
70 kfree_sensitive(objp: buffer);
71 return ret;
72}
73EXPORT_SYMBOL(crypto_krb5_calc_PRFplus);
74
75/**
76 * krb5_derive_Kc - Derive key Kc and install into a hash
77 * @krb5: The encryption type to use
78 * @TK: The base key
79 * @usage: The key usage number
80 * @key: Prepped buffer to store the key into
81 * @gfp: Allocation restrictions
82 *
83 * Derive the Kerberos Kc checksumming key. The key is stored into the
84 * prepared buffer.
85 */
86int krb5_derive_Kc(const struct krb5_enctype *krb5, const struct krb5_buffer *TK,
87 u32 usage, struct krb5_buffer *key, gfp_t gfp)
88{
89 u8 buf[5] __aligned(CRYPTO_MINALIGN);
90 struct krb5_buffer usage_constant = { .len = 5, .data = buf };
91
92 *(__be32 *)buf = cpu_to_be32(usage);
93 buf[4] = KEY_USAGE_SEED_CHECKSUM;
94
95 key->len = krb5->Kc_len;
96 return krb5->profile->calc_Kc(krb5, TK, &usage_constant, key, gfp);
97}
98
99/**
100 * krb5_derive_Ke - Derive key Ke and install into an skcipher
101 * @krb5: The encryption type to use
102 * @TK: The base key
103 * @usage: The key usage number
104 * @key: Prepped buffer to store the key into
105 * @gfp: Allocation restrictions
106 *
107 * Derive the Kerberos Ke encryption key. The key is stored into the prepared
108 * buffer.
109 */
110int krb5_derive_Ke(const struct krb5_enctype *krb5, const struct krb5_buffer *TK,
111 u32 usage, struct krb5_buffer *key, gfp_t gfp)
112{
113 u8 buf[5] __aligned(CRYPTO_MINALIGN);
114 struct krb5_buffer usage_constant = { .len = 5, .data = buf };
115
116 *(__be32 *)buf = cpu_to_be32(usage);
117 buf[4] = KEY_USAGE_SEED_ENCRYPTION;
118
119 key->len = krb5->Ke_len;
120 return krb5->profile->calc_Ke(krb5, TK, &usage_constant, key, gfp);
121}
122
123/**
124 * krb5_derive_Ki - Derive key Ki and install into a hash
125 * @krb5: The encryption type to use
126 * @TK: The base key
127 * @usage: The key usage number
128 * @key: Prepped buffer to store the key into
129 * @gfp: Allocation restrictions
130 *
131 * Derive the Kerberos Ki integrity checksum key. The key is stored into the
132 * prepared buffer.
133 */
134int krb5_derive_Ki(const struct krb5_enctype *krb5, const struct krb5_buffer *TK,
135 u32 usage, struct krb5_buffer *key, gfp_t gfp)
136{
137 u8 buf[5] __aligned(CRYPTO_MINALIGN);
138 struct krb5_buffer usage_constant = { .len = 5, .data = buf };
139
140 *(__be32 *)buf = cpu_to_be32(usage);
141 buf[4] = KEY_USAGE_SEED_INTEGRITY;
142
143 key->len = krb5->Ki_len;
144 return krb5->profile->calc_Ki(krb5, TK, &usage_constant, key, gfp);
145}
146

source code of linux/crypto/krb5/krb5_kdf.c