[PATCH 03/18] crypto/krb5: Provide infrastructure and key derivation

[David Howells <dhowells@redhat.com>]

Provide key derivation interface functions and a helper to implement the
PRF+ function from rfc4402.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 crypto/krb5/Makefile  |    1 
 crypto/krb5/kdf.c     |  223 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/crypto/krb5.h |   29 ++++++
 3 files changed, 253 insertions(+)
 create mode 100644 crypto/krb5/kdf.c

diff --git a/crypto/krb5/Makefile b/crypto/krb5/Makefile
index 071ce2ff82e5..b764c4d09bf2 100644
--- a/crypto/krb5/Makefile
+++ b/crypto/krb5/Makefile
@@ -4,6 +4,7 @@
 #
 
 krb5-y += \
+	kdf.o \
 	main.o
 
 obj-$(CONFIG_CRYPTO_KRB5) += krb5.o
diff --git a/crypto/krb5/kdf.c b/crypto/krb5/kdf.c
new file mode 100644
index 000000000000..8ef7ea31ee8a
--- /dev/null
+++ b/crypto/krb5/kdf.c
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Kerberos key derivation.
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/export.h>
+#include <linux/slab.h>
+#include <crypto/skcipher.h>
+#include <crypto/hash.h>
+#include "internal.h"
+
+/**
+ * crypto_krb5_free_enc_keys - Free an encryption keypair
+ * @e: The key pair to free.
+ */
+void crypto_krb5_free_enc_keys(struct krb5_enc_keys *e)
+{
+	if (e->Ke)
+		crypto_free_sync_skcipher(e->Ke);
+	if (e->Ki)
+		crypto_free_shash(e->Ki);
+	e->Ke = NULL;
+	e->Ki = NULL;
+}
+EXPORT_SYMBOL(crypto_krb5_free_enc_keys);
+
+/**
+ * crypto_krb5_calc_PRFplus - Calculate PRF+ [RFC4402]
+ * @krb5: The encryption type to use
+ * @K: The protocol key for the pseudo-random function
+ * @L: The length of the output
+ * @S: The input octet string
+ * @result: Result buffer, sized to krb5->prf_len
+ * @gfp: Allocation restrictions
+ *
+ * Calculate the kerberos pseudo-random function, PRF+() by the following
+ * method:
+ *
+ *      PRF+(K, L, S) = truncate(L, T1 || T2 || .. || Tn)
+ *      Tn = PRF(K, n || S)
+ *      [rfc4402 sec 2]
+ */
+int crypto_krb5_calc_PRFplus(const struct krb5_enctype *krb5,
+			     const struct krb5_buffer *K,
+			     unsigned int L,
+			     const struct krb5_buffer *S,
+			     struct krb5_buffer *result,
+			     gfp_t gfp)
+{
+	struct krb5_buffer T_series, Tn, n_S;
+	void *buffer;
+	int ret, n = 1;
+
+	Tn.len = krb5->prf_len;
+	T_series.len = 0;
+	n_S.len = 4 + S->len;
+
+	buffer = kzalloc(round16(L + Tn.len) + round16(n_S.len), gfp);
+	if (!buffer)
+		return -ENOMEM;
+
+	T_series.data = buffer;
+	n_S.data = buffer + round16(L + Tn.len);
+	memcpy(n_S.data + 4, S->data, S->len);
+
+	while (T_series.len < L) {
+		*(__be32 *)(n_S.data) = htonl(n);
+		Tn.data = T_series.data + Tn.len * (n - 1);
+		ret = krb5->profile->calc_PRF(krb5, K, &n_S, &Tn, gfp);
+		if (ret < 0)
+			goto err;
+		T_series.len += Tn.len;
+		n++;
+	}
+
+	/* Truncate to L */
+	memcpy(result->data, T_series.data, L);
+	ret = 0;
+
+err:
+	kfree_sensitive(buffer);
+	return ret;
+}
+EXPORT_SYMBOL(crypto_krb5_calc_PRFplus);
+
+/**
+ * crypto_krb5_get_Kc - Derive key Kc and install into a hash
+ * @krb5: The encryption type to use
+ * @TK: The base key
+ * @usage: The key usage number
+ * @key: Prepped buffer to store the key into
+ * @_shash: Where to put the hash (or NULL if not wanted)
+ * @gfp: Allocation restrictions
+ *
+ * Derive the Kerberos Kc checksumming key and, optionally, allocate a hash and
+ * install the key into it, returning the hash.  The key is stored into the
+ * prepared buffer.
+ */
+int crypto_krb5_get_Kc(const struct krb5_enctype *krb5,
+		       const struct krb5_buffer *TK,
+		       u32 usage,
+		       struct krb5_buffer *key,
+		       struct crypto_shash **_shash,
+		       gfp_t gfp)
+{
+	struct crypto_shash *shash;
+	int ret;
+	u8 buf[CRYPTO_MINALIGN] __aligned(CRYPTO_MINALIGN);
+	struct krb5_buffer usage_constant = { .len = 5, .data = buf };
+
+	*(__be32 *)buf = cpu_to_be32(usage);
+	buf[4] = KEY_USAGE_SEED_CHECKSUM;
+
+	key->len = krb5->Kc_len;
+	ret = krb5->profile->calc_Kc(krb5, TK, &usage_constant, key, gfp);
+	if (ret < 0)
+		return ret;
+
+	if (_shash) {
+		shash = crypto_alloc_shash(krb5->cksum_name, 0, 0);
+		if (IS_ERR(shash))
+			return (PTR_ERR(shash) == -ENOENT) ? -ENOPKG : PTR_ERR(shash);
+		*_shash = shash;
+		ret = crypto_shash_setkey(shash, key->data, key->len);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(crypto_krb5_get_Kc);
+
+/**
+ * crypto_krb5_get_Ke - Derive key Ke and install into an skcipher
+ * @krb5: The encryption type to use
+ * @TK: The base key
+ * @usage: The key usage number
+ * @key: Prepped buffer to store the key into
+ * @_ci: Where to put the cipher (or NULL if not wanted)
+ * @gfp: Allocation restrictions
+ *
+ * Derive the Kerberos Ke encryption key and, optionally, allocate an skcipher
+ * and install the key into it, returning the cipher.  The key is stored into
+ * the prepared buffer.
+ */
+int crypto_krb5_get_Ke(const struct krb5_enctype *krb5,
+		       const struct krb5_buffer *TK,
+		       u32 usage,
+		       struct krb5_buffer *key,
+		       struct crypto_sync_skcipher **_ci,
+		       gfp_t gfp)
+{
+	struct crypto_sync_skcipher *ci;
+	int ret;
+	u8 buf[CRYPTO_MINALIGN] __aligned(CRYPTO_MINALIGN);
+	struct krb5_buffer usage_constant = { .len = 5, .data = buf };
+
+	*(__be32 *)buf = cpu_to_be32(usage);
+	buf[4] = KEY_USAGE_SEED_ENCRYPTION;
+
+	key->len = krb5->Ke_len;
+	ret = krb5->profile->calc_Ke(krb5, TK, &usage_constant, key, gfp);
+	if (ret < 0)
+		return ret;
+
+	if (_ci) {
+		ci = crypto_alloc_sync_skcipher(krb5->encrypt_name, 0, 0);
+		if (IS_ERR(ci))
+			return (PTR_ERR(ci) == -ENOENT) ? -ENOPKG : PTR_ERR(ci);
+		*_ci = ci;
+		ret = crypto_sync_skcipher_setkey(ci, key->data, key->len);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(crypto_krb5_get_Ke);
+
+/**
+ * crypto_krb5_get_Ki - Derive key Ki and install into a hash
+ * @krb5: The encryption type to use
+ * @TK: The base key
+ * @usage: The key usage number
+ * @key: Prepped buffer to store the key into
+ * @_shash: Where to put the hash (or NULL if not wanted)
+ * @gfp: Allocation restrictions
+ *
+ * Derive the Kerberos Ki integrity checksum key and, optionally, allocate a
+ * hash and install the key into it, returning the hash.  The key is stored
+ * into the prepared buffer.
+ */
+int crypto_krb5_get_Ki(const struct krb5_enctype *krb5,
+		       const struct krb5_buffer *TK,
+		       u32 usage,
+		       struct krb5_buffer *key,
+		       struct crypto_shash **_shash,
+		       gfp_t gfp)
+{
+	struct crypto_shash *shash;
+	int ret;
+	u8 buf[CRYPTO_MINALIGN] __aligned(CRYPTO_MINALIGN);
+	struct krb5_buffer usage_constant = { .len = 5, .data = buf };
+
+	*(__be32 *)buf = cpu_to_be32(usage);
+	buf[4] = KEY_USAGE_SEED_INTEGRITY;
+
+	key->len = krb5->Ki_len;
+	ret = krb5->profile->calc_Kc(krb5, TK, &usage_constant, key, gfp);
+	if (ret < 0)
+		return ret;
+
+	if (_shash) {
+		shash = crypto_alloc_shash(krb5->cksum_name, 0, 0);
+		if (IS_ERR(shash))
+			return (PTR_ERR(shash) == -ENOENT) ? -ENOPKG : PTR_ERR(shash);
+		*_shash = shash;
+		ret = crypto_shash_setkey(shash, key->data, key->len);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(crypto_krb5_get_Ki);
diff --git a/include/crypto/krb5.h b/include/crypto/krb5.h
index a7e4ab4e1348..04286bacaf06 100644
--- a/include/crypto/krb5.h
+++ b/include/crypto/krb5.h
@@ -103,4 +103,33 @@ struct krb5_enctype {
  */
 extern const struct krb5_enctype *crypto_krb5_find_enctype(u32 enctype);
 
+/*
+ * kdf.c
+ */
+extern void crypto_krb5_free_enc_keys(struct krb5_enc_keys *e);
+extern int crypto_krb5_calc_PRFplus(const struct krb5_enctype *krb5,
+				    const struct krb5_buffer *K,
+				    unsigned int L,
+				    const struct krb5_buffer *S,
+				    struct krb5_buffer *result,
+				    gfp_t gfp);
+extern int crypto_krb5_get_Kc(const struct krb5_enctype *krb5,
+			      const struct krb5_buffer *TK,
+			      u32 usage,
+			      struct krb5_buffer *key,
+			      struct crypto_shash **_shash,
+			      gfp_t gfp);
+extern int crypto_krb5_get_Ke(const struct krb5_enctype *krb5,
+			      const struct krb5_buffer *TK,
+			      u32 usage,
+			      struct krb5_buffer *key,
+			      struct crypto_sync_skcipher **_ci,
+			      gfp_t gfp);
+extern int crypto_krb5_get_Ki(const struct krb5_enctype *krb5,
+			      const struct krb5_buffer *TK,
+			      u32 usage,
+			      struct krb5_buffer *key,
+			      struct crypto_shash **_shash,
+			      gfp_t gfp);
+
 #endif /* _CRYPTO_KRB5_H */