lib/crypto: aes: Add ECB support

Add support for AES-ECB to the crypto library.

This will be used to provide a streamlined implementation of the
"ecb(aes)" crypto_skcipher algorithm.  fs/crypto/keysetup_v1.c will also
use aes_ecb_encrypt() directly.

As usual, the architecture-optimized AES-ECB code will be migrated into
the library as well (using the hooks provided in this commit),
eliminating lots of repetitive boilerplate code.

ECB is obsolete of course, but we need this for parity with the
traditional API and to support some odd users of ECB in the kernel.

Initial test coverage is provided by the crypto_skcipher support added
in a later commit.  I'm planning a KUnit test suite as well.

Create a documentation file libcrypto-unauth-encryption.rst to hold the
documentation for this and other unauthenticated encryption modes.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Link: https://patch.msgid.link/20260715221153.246410-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/include/crypto/aes-ecb.h b/include/crypto/aes-ecb.h
new file mode 100644
index 000000000000..8cac1f8794c7
--- /dev/null
+++ b/include/crypto/aes-ecb.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * AES-ECB unauthenticated encryption and decryption
+ *
+ * Copyright 2026 Google LLC
+ */
+#ifndef _CRYPTO_AES_ECB_H
+#define _CRYPTO_AES_ECB_H
+
+#include <crypto/aes.h>
+
+/**
+ * aes_ecb_encrypt() - Encrypt data using AES-ECB
+ * @dst: The destination buffer.  Can be in-place or out-of-place.  For other
+ *	 overlaps the behavior is unspecified.
+ * @src: The source data
+ * @len: Number of bytes to encrypt.  Must be a multiple of AES_BLOCK_SIZE.
+ * @key: The key, already prepared using aes_preparekey() or aes_prepareenckey()
+ *
+ * ECB mode is insecure by itself.  This function exists only for compatibility
+ * with legacy protocols and for internal use by other modes.
+ *
+ * This supports incremental encryption, but the length of each chunk must be a
+ * multiple of AES_BLOCK_SIZE.
+ *
+ * Context: Any context.
+ */
+void aes_ecb_encrypt(u8 *dst, const u8 *src, size_t len, aes_encrypt_arg key);
+
+/**
+ * aes_ecb_decrypt() - Decrypt data using AES-ECB
+ * @dst: The destination buffer.  Can be in-place or out-of-place.  For other
+ *	 overlaps the behavior is unspecified.
+ * @src: The source data
+ * @len: Number of bytes to decrypt.  Must be a multiple of AES_BLOCK_SIZE.
+ * @key: The key, already prepared using aes_preparekey()
+ *
+ * ECB mode is insecure by itself.  This function exists only for compatibility
+ * with legacy protocols and for internal use by other modes.
+ *
+ * This supports incremental decryption, but the length of each chunk must be a
+ * multiple of AES_BLOCK_SIZE.
+ *
+ * Context: Any context.
+ */
+void aes_ecb_decrypt(u8 *dst, const u8 *src, size_t len,
+		     const struct aes_key *key);
+
+#endif /* _CRYPTO_AES_ECB_H */