crypto/krb5: Implement Kerberos crypto core

Provide core structures, an encoding-type registry and basic module and
config bits for a generic Kerberos crypto library.

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

6 files changed, 180 insertions, 0 deletions

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 15a6730d3ea1..f0119d92decc 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1472,5 +1472,6 @@ endif
 source "drivers/crypto/Kconfig"
 source "crypto/asymmetric_keys/Kconfig"
 source "certs/Kconfig"
+source "crypto/krb5/Kconfig"
 
 endif	# if CRYPTO
diff --git a/crypto/Makefile b/crypto/Makefile
index 20c8e3ee9835..d1e422249af6 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -213,3 +213,5 @@ obj-$(CONFIG_CRYPTO_SIMD) += crypto_simd.o
 # Key derivation function
 #
 obj-$(CONFIG_CRYPTO_KDF800108_CTR) += kdf_sp800108.o
+
+obj-$(CONFIG_CRYPTO_KRB5) += krb5/
diff --git a/crypto/krb5/Kconfig b/crypto/krb5/Kconfig
new file mode 100644
index 000000000000..079873618abf
--- /dev/null
+++ b/crypto/krb5/Kconfig
@@ -0,0 +1,14 @@
+config CRYPTO_KRB5
+	tristate "Kerberos 5 crypto"
+	select CRYPTO_MANAGER
+	select CRYPTO_KRB5ENC
+	select CRYPTO_AUTHENC
+	select CRYPTO_SKCIPHER
+	select CRYPTO_HASH_INFO
+	select CRYPTO_SHA1
+	select CRYPTO_CBC
+	select CRYPTO_CTS
+	select CRYPTO_AES
+	help
+	  Provide a library for provision of Kerberos-5-based crypto.  This is
+	  intended for network filesystems to use.
diff --git a/crypto/krb5/Makefile b/crypto/krb5/Makefile
new file mode 100644
index 000000000000..c450d0754772
--- /dev/null
+++ b/crypto/krb5/Makefile
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for asymmetric cryptographic keys
+#
+
+krb5-y += \
+	krb5_api.o
+
+obj-$(CONFIG_CRYPTO_KRB5) += krb5.o
diff --git a/crypto/krb5/internal.h b/crypto/krb5/internal.h
new file mode 100644
index 000000000000..3ede858be4f7
--- /dev/null
+++ b/crypto/krb5/internal.h
@@ -0,0 +1,112 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Kerberos5 crypto internals
+ *
+ * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <crypto/krb5.h>
+
+/*
+ * Profile used for key derivation and encryption.
+ */
+struct krb5_crypto_profile {
+	 /* Pseudo-random function */
+	int (*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);
+
+	/* Checksum key derivation */
+	int (*calc_Kc)(const struct krb5_enctype *krb5,
+		       const struct krb5_buffer *TK,
+		       const struct krb5_buffer *usage_constant,
+		       struct krb5_buffer *Kc,
+		       gfp_t gfp);
+
+	/* Encryption key derivation */
+	int (*calc_Ke)(const struct krb5_enctype *krb5,
+		       const struct krb5_buffer *TK,
+		       const struct krb5_buffer *usage_constant,
+		       struct krb5_buffer *Ke,
+		       gfp_t gfp);
+
+	 /* Integrity key derivation */
+	int (*calc_Ki)(const struct krb5_enctype *krb5,
+		       const struct krb5_buffer *TK,
+		       const struct krb5_buffer *usage_constant,
+		       struct krb5_buffer *Ki,
+		       gfp_t gfp);
+
+	/* Derive the keys needed for an encryption AEAD object. */
+	int (*derive_encrypt_keys)(const struct krb5_enctype *krb5,
+				   const struct krb5_buffer *TK,
+				   unsigned int usage,
+				   struct krb5_buffer *setkey,
+				   gfp_t gfp);
+
+	/* Directly load the keys needed for an encryption AEAD object. */
+	int (*load_encrypt_keys)(const struct krb5_enctype *krb5,
+				 const struct krb5_buffer *Ke,
+				 const struct krb5_buffer *Ki,
+				 struct krb5_buffer *setkey,
+				 gfp_t gfp);
+
+	/* Derive the key needed for a checksum hash object. */
+	int (*derive_checksum_key)(const struct krb5_enctype *krb5,
+				   const struct krb5_buffer *TK,
+				   unsigned int usage,
+				   struct krb5_buffer *setkey,
+				   gfp_t gfp);
+
+	/* Directly load the keys needed for a checksum hash object. */
+	int (*load_checksum_key)(const struct krb5_enctype *krb5,
+				 const struct krb5_buffer *Kc,
+				 struct krb5_buffer *setkey,
+				 gfp_t gfp);
+
+	/* Encrypt data in-place, inserting confounder and checksum. */
+	ssize_t (*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);
+
+	/* Decrypt data in-place, removing confounder and checksum */
+	int (*decrypt)(const struct krb5_enctype *krb5,
+		       struct crypto_aead *aead,
+		       struct scatterlist *sg, unsigned int nr_sg,
+		       size_t *_offset, size_t *_len);
+
+	/* Generate a MIC on part of a packet, inserting the checksum */
+	ssize_t (*get_mic)(const struct krb5_enctype *krb5,
+			   struct crypto_shash *shash,
+			   const struct krb5_buffer *metadata,
+			   struct scatterlist *sg, unsigned int nr_sg,
+			   size_t sg_len,
+			   size_t data_offset, size_t data_len);
+
+	/* Verify the MIC on a piece of data, removing the checksum */
+	int (*verify_mic)(const struct krb5_enctype *krb5,
+			  struct crypto_shash *shash,
+			  const struct krb5_buffer *metadata,
+			  struct scatterlist *sg, unsigned int nr_sg,
+			  size_t *_offset, size_t *_len);
+};
+
+/*
+ * Crypto size/alignment rounding convenience macros.
+ */
+#define crypto_roundup(X) ((unsigned int)round_up((X), CRYPTO_MINALIGN))
+
+#define krb5_aead_size(TFM) \
+	crypto_roundup(sizeof(struct aead_request) + crypto_aead_reqsize(TFM))
+#define krb5_aead_ivsize(TFM) \
+	crypto_roundup(crypto_aead_ivsize(TFM))
+#define krb5_shash_size(TFM) \
+	crypto_roundup(sizeof(struct shash_desc) + crypto_shash_descsize(TFM))
+#define krb5_digest_size(TFM) \
+	crypto_roundup(crypto_shash_digestsize(TFM))
+#define round16(x) (((x) + 15) & ~15)
diff --git a/crypto/krb5/krb5_api.c b/crypto/krb5/krb5_api.c
new file mode 100644
index 000000000000..5c1cd5d07fc3
--- /dev/null
+++ b/crypto/krb5/krb5_api.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Kerberos 5 crypto library.
+ *
+ * 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/module.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include "internal.h"
+
+MODULE_DESCRIPTION("Kerberos 5 crypto");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+static const struct krb5_enctype *const krb5_supported_enctypes[] = {
+};
+
+/**
+ * crypto_krb5_find_enctype - Find the handler for a Kerberos5 encryption type
+ * @enctype: The standard Kerberos encryption type number
+ *
+ * Look up a Kerberos encryption type by number.  If successful, returns a
+ * pointer to the type tables; returns NULL otherwise.
+ */
+const struct krb5_enctype *crypto_krb5_find_enctype(u32 enctype)
+{
+	const struct krb5_enctype *krb5;
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(krb5_supported_enctypes); i++) {
+		krb5 = krb5_supported_enctypes[i];
+		if (krb5->etype == enctype)
+			return krb5;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL(crypto_krb5_find_enctype);