--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* rfc8009 AES Encryption with HMAC-SHA2 for Kerberos 5
+ *
+ * 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 <crypto/authenc.h>
+#include "internal.h"
+
+static const struct krb5_buffer rfc8009_no_context = { .len = 0, .data = "" };
+
+/*
+ * Calculate the key derivation function KDF-HMAC-SHA2(key, label, [context,] k)
+ *
+ * KDF-HMAC-SHA2(key, label, [context,] k) = k-truncate(K1)
+ *
+ * Using the appropriate one of:
+ * K1 = HMAC-SHA-256(key, 0x00000001 | label | 0x00 | k)
+ * K1 = HMAC-SHA-384(key, 0x00000001 | label | 0x00 | k)
+ * K1 = HMAC-SHA-256(key, 0x00000001 | label | 0x00 | context | k)
+ * K1 = HMAC-SHA-384(key, 0x00000001 | label | 0x00 | context | k)
+ * [rfc8009 sec 3]
+ */
+static int rfc8009_calc_KDF_HMAC_SHA2(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *key,
+ const struct krb5_buffer *label,
+ const struct krb5_buffer *context,
+ unsigned int k,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ struct crypto_shash *shash;
+ struct krb5_buffer K1, data;
+ struct shash_desc *desc;
+ __be32 tmp;
+ size_t bsize;
+ void *buffer;
+ u8 *p;
+ int ret = -ENOMEM;
+
+ if (WARN_ON(result->len != k / 8))
+ return -EINVAL;
+
+ shash = crypto_alloc_shash(krb5->cksum_name, 0, 0);
+ if (IS_ERR(shash))
+ return (PTR_ERR(shash) == -ENOENT) ? -ENOPKG : PTR_ERR(shash);
+ ret = crypto_shash_setkey(shash, key->data, key->len);
+ if (ret < 0)
+ goto error_shash;
+
+ ret = -EINVAL;
+ if (WARN_ON(crypto_shash_digestsize(shash) * 8 < k))
+ goto error_shash;
+
+ ret = -ENOMEM;
+ data.len = 4 + label->len + 1 + context->len + 4;
+ bsize = krb5_shash_size(shash) +
+ krb5_digest_size(shash) +
+ crypto_roundup(data.len);
+ buffer = kzalloc(bsize, GFP_NOFS);
+ if (!buffer)
+ goto error_shash;
+
+ desc = buffer;
+ desc->tfm = shash;
+ ret = crypto_shash_init(desc);
+ if (ret < 0)
+ goto error;
+
+ p = data.data = buffer +
+ krb5_shash_size(shash) +
+ krb5_digest_size(shash);
+ *(__be32 *)p = htonl(0x00000001);
+ p += 4;
+ memcpy(p, label->data, label->len);
+ p += label->len;
+ *p++ = 0;
+ memcpy(p, context->data, context->len);
+ p += context->len;
+ tmp = htonl(k);
+ memcpy(p, &tmp, 4);
+ p += 4;
+
+ ret = -EINVAL;
+ if (WARN_ON(p - (u8 *)data.data != data.len))
+ goto error;
+
+ K1.len = crypto_shash_digestsize(shash);
+ K1.data = buffer +
+ krb5_shash_size(shash);
+
+ ret = crypto_shash_finup(desc, data.data, data.len, K1.data);
+ if (ret < 0)
+ goto error;
+
+ memcpy(result->data, K1.data, result->len);
+
+error:
+ kfree_sensitive(buffer);
+error_shash:
+ crypto_free_shash(shash);
+ return ret;
+}
+
+/*
+ * Calculate the pseudo-random function, PRF().
+ *
+ * PRF = KDF-HMAC-SHA2(input-key, "prf", octet-string, 256)
+ * PRF = KDF-HMAC-SHA2(input-key, "prf", octet-string, 384)
+ *
+ * The "prfconstant" used in the PRF operation is the three-octet string
+ * "prf".
+ * [rfc8009 sec 5]
+ */
+static int rfc8009_calc_PRF(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *input_key,
+ const struct krb5_buffer *octet_string,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ static const struct krb5_buffer prfconstant = { 3, "prf" };
+
+ return rfc8009_calc_KDF_HMAC_SHA2(krb5, input_key, &prfconstant,
+ octet_string, krb5->prf_len * 8,
+ result, gfp);
+}
+
+/*
+ * Derive Ke.
+ * Ke = KDF-HMAC-SHA2(base-key, usage | 0xAA, 128)
+ * Ke = KDF-HMAC-SHA2(base-key, usage | 0xAA, 256)
+ * [rfc8009 sec 5]
+ */
+static int rfc8009_calc_Ke(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *base_key,
+ const struct krb5_buffer *usage_constant,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ return rfc8009_calc_KDF_HMAC_SHA2(krb5, base_key, usage_constant,
+ &rfc8009_no_context, krb5->key_bytes * 8,
+ result, gfp);
+}
+
+/*
+ * Derive Kc/Ki
+ * Kc = KDF-HMAC-SHA2(base-key, usage | 0x99, 128)
+ * Ki = KDF-HMAC-SHA2(base-key, usage | 0x55, 128)
+ * Kc = KDF-HMAC-SHA2(base-key, usage | 0x99, 192)
+ * Ki = KDF-HMAC-SHA2(base-key, usage | 0x55, 192)
+ * [rfc8009 sec 5]
+ */
+static int rfc8009_calc_Ki(const struct krb5_enctype *krb5,
+ const struct krb5_buffer *base_key,
+ const struct krb5_buffer *usage_constant,
+ struct krb5_buffer *result,
+ gfp_t gfp)
+{
+ return rfc8009_calc_KDF_HMAC_SHA2(krb5, base_key, usage_constant,
+ &rfc8009_no_context, krb5->cksum_len * 8,
+ result, gfp);
+}
+
+/*
+ * Apply encryption and checksumming functions to a message. Unlike for
+ * RFC3961, for RFC8009, we have to chuck the starting IV into the hash first.
+ */
+static ssize_t rfc8009_encrypt(const struct krb5_enctype *krb5,
+ struct crypto_aead *aead,
+ struct scatterlist *sg, unsigned int nr_sg, size_t sg_len,
+ size_t data_offset, size_t data_len,
+ bool preconfounded)
+{
+ struct aead_request *req;
+ struct scatterlist bsg[2];
+ ssize_t ret, done;
+ size_t bsize, base_len, secure_offset, secure_len, pad_len, cksum_offset;
+ void *buffer;
+ u8 *iv, *ad;
+
+ if (WARN_ON(data_offset != krb5->conf_len))
+ return -EINVAL; /* Data is in wrong place */
+
+ secure_offset = 0;
+ base_len = krb5->conf_len + data_len;
+ pad_len = 0;
+ secure_len = base_len + pad_len;
+ cksum_offset = secure_len;
+ if (WARN_ON(cksum_offset + krb5->cksum_len > sg_len))
+ return -EFAULT;
+
+ bsize = krb5_aead_size(aead) +
+ krb5_aead_ivsize(aead) * 2;
+ buffer = kzalloc(bsize, GFP_NOFS);
+ if (!buffer)
+ return -ENOMEM;
+
+ req = buffer;
+ iv = buffer + krb5_aead_size(aead);
+ ad = buffer + krb5_aead_size(aead) + krb5_aead_ivsize(aead);
+
+ /* Insert the confounder into the buffer */
+ ret = -EFAULT;
+ if (!preconfounded) {
+ get_random_bytes(buffer, krb5->conf_len);
+ done = sg_pcopy_from_buffer(sg, nr_sg, buffer, krb5->conf_len,
+ secure_offset);
+ if (done != krb5->conf_len)
+ goto error;
+ }
+
+ /* We may need to pad out to the crypto blocksize. */
+ if (pad_len) {
+ done = sg_zero_buffer(sg, nr_sg, pad_len, data_offset + data_len);
+ if (done != pad_len)
+ goto error;
+ }
+
+ /* We need to include the starting IV in the hash. */
+ sg_init_table(bsg, 2);
+ sg_set_buf(&bsg[0], ad, krb5_aead_ivsize(aead));
+ sg_chain(bsg, 2, sg);
+
+ /* Hash and encrypt the message. */
+ aead_request_set_tfm(req, aead);
+ aead_request_set_callback(req, 0, NULL, NULL);
+ aead_request_set_ad(req, krb5_aead_ivsize(aead));
+ aead_request_set_crypt(req, bsg, bsg, secure_len, iv);
+ ret = crypto_aead_encrypt(req);
+ if (ret < 0)
+ goto error;
+
+ ret = secure_len + krb5->cksum_len;
+
+error:
+ kfree_sensitive(buffer);
+ return ret;
+}
+
+/*
+ * Apply decryption and checksumming functions to a message. Unlike for
+ * RFC3961, for RFC8009, we have to chuck the starting IV into the hash first.
+ *
+ * The offset and length are updated to reflect the actual content of the
+ * encrypted region.
+ */
+static int rfc8009_decrypt(const struct krb5_enctype *krb5,
+ struct crypto_aead *aead,
+ struct scatterlist *sg, unsigned int nr_sg,
+ size_t *_offset, size_t *_len)
+{
+ struct aead_request *req;
+ struct scatterlist bsg[2];
+ size_t bsize;
+ void *buffer;
+ int ret;
+ u8 *iv, *ad;
+
+ if (WARN_ON(*_offset != 0))
+ return -EINVAL; /* Can't set offset on aead */
+
+ if (*_len < krb5->conf_len + krb5->cksum_len)
+ return -EPROTO;
+
+ bsize = krb5_aead_size(aead) +
+ krb5_aead_ivsize(aead) * 2;
+ buffer = kzalloc(bsize, GFP_NOFS);
+ if (!buffer)
+ return -ENOMEM;
+
+ req = buffer;
+ iv = buffer + krb5_aead_size(aead);
+ ad = buffer + krb5_aead_size(aead) + krb5_aead_ivsize(aead);
+
+ /* We need to include the starting IV in the hash. */
+ sg_init_table(bsg, 2);
+ sg_set_buf(&bsg[0], ad, krb5_aead_ivsize(aead));
+ sg_chain(bsg, 2, sg);
+
+ /* Decrypt the message and verify its checksum. */
+ aead_request_set_tfm(req, aead);
+ aead_request_set_callback(req, 0, NULL, NULL);
+ aead_request_set_ad(req, krb5_aead_ivsize(aead));
+ aead_request_set_crypt(req, bsg, bsg, *_len, iv);
+ ret = crypto_aead_decrypt(req);
+ if (ret < 0)
+ goto error;
+
+ /* Adjust the boundaries of the data. */
+ *_offset += krb5->conf_len;
+ *_len -= krb5->conf_len + krb5->cksum_len;
+ ret = 0;
+
+error:
+ kfree_sensitive(buffer);
+ return ret;
+}
+
+static const struct krb5_crypto_profile rfc8009_crypto_profile = {
+ .calc_PRF = rfc8009_calc_PRF,
+ .calc_Kc = rfc8009_calc_Ki,
+ .calc_Ke = rfc8009_calc_Ke,
+ .calc_Ki = rfc8009_calc_Ki,
+ .derive_encrypt_keys = authenc_derive_encrypt_keys,
+ .load_encrypt_keys = authenc_load_encrypt_keys,
+ .derive_checksum_key = rfc3961_derive_checksum_key,
+ .load_checksum_key = rfc3961_load_checksum_key,
+ .encrypt = rfc8009_encrypt,
+ .decrypt = rfc8009_decrypt,
+ .get_mic = rfc3961_get_mic,
+ .verify_mic = rfc3961_verify_mic,
+};
+
+const struct krb5_enctype krb5_aes128_cts_hmac_sha256_128 = {
+ .etype = KRB5_ENCTYPE_AES128_CTS_HMAC_SHA256_128,
+ .ctype = KRB5_CKSUMTYPE_HMAC_SHA256_128_AES128,
+ .name = "aes128-cts-hmac-sha256-128",
+ .encrypt_name = "authenc(hmac(sha256),cts(cbc(aes)))",
+ .cksum_name = "hmac(sha256)",
+ .hash_name = "sha256",
+ .derivation_enc = "cts(cbc(aes))",
+ .key_bytes = 16,
+ .key_len = 16,
+ .Kc_len = 16,
+ .Ke_len = 16,
+ .Ki_len = 16,
+ .block_len = 16,
+ .conf_len = 16,
+ .cksum_len = 16,
+ .hash_len = 20,
+ .prf_len = 32,
+ .keyed_cksum = true,
+ .random_to_key = NULL, /* Identity */
+ .profile = &rfc8009_crypto_profile,
+};
+
+const struct krb5_enctype krb5_aes256_cts_hmac_sha384_192 = {
+ .etype = KRB5_ENCTYPE_AES256_CTS_HMAC_SHA384_192,
+ .ctype = KRB5_CKSUMTYPE_HMAC_SHA384_192_AES256,
+ .name = "aes256-cts-hmac-sha384-192",
+ .encrypt_name = "authenc(hmac(sha384),cts(cbc(aes)))",
+ .cksum_name = "hmac(sha384)",
+ .hash_name = "sha384",
+ .derivation_enc = "cts(cbc(aes))",
+ .key_bytes = 32,
+ .key_len = 32,
+ .Kc_len = 24,
+ .Ke_len = 32,
+ .Ki_len = 24,
+ .block_len = 16,
+ .conf_len = 16,
+ .cksum_len = 24,
+ .hash_len = 20,
+ .prf_len = 48,
+ .keyed_cksum = true,
+ .random_to_key = NULL, /* Identity */
+ .profile = &rfc8009_crypto_profile,
+};
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