[crypto] Add concept of cipher alignment size

The GCM cipher mode of operation (in common with other counter-based
modes of operation) has a notion of blocksize that does not neatly
fall into our current abstraction: it does operate in 16-byte blocks
but allows for an arbitrary overall data length (i.e. the final block
may be incomplete).

Model this by adding a concept of alignment size.  Each call to
encrypt() or decrypt() must begin at a multiple of the alignment size
from the start of the data stream.  This allows us to model GCM by
using a block size of 1 byte and an alignment size of 16 bytes.

As a side benefit, this same concept allows us to neatly model the
fact that raw AES can encrypt only a single 16-byte block, by
specifying an alignment size of zero on this cipher.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/crypto/aes.c

@@ -784,6 +784,7 @@ struct cipher_algorithm aes_algorithm = {
 	.name = "aes",
 	.ctxsize = sizeof ( struct aes_context ),
 	.blocksize = AES_BLOCKSIZE,
+	.alignsize = 0,
 	.authsize = 0,
 	.setkey = aes_setkey,
 	.setiv = cipher_null_setiv,

src/crypto/arc4.c

@@ -119,6 +119,7 @@ struct cipher_algorithm arc4_algorithm = {
 	.name = "ARC4",
 	.ctxsize = ARC4_CTX_SIZE,
 	.blocksize = 1,
+	.alignsize = 1,
 	.authsize = 0,
 	.setkey = arc4_setkey,
 	.setiv = cipher_null_setiv,

src/crypto/crypto_null.c

@@ -84,6 +84,7 @@ struct cipher_algorithm cipher_null = {
 	.name = "null",
 	.ctxsize = 0,
 	.blocksize = 1,
+	.alignsize = 1,
 	.authsize = 0,
 	.setkey = cipher_null_setkey,
 	.setiv = cipher_null_setiv,

src/include/ipxe/cbc.h

@@ -95,6 +95,7 @@ struct cipher_algorithm _cbc_cipher = {					\
 	.name		= #_cbc_name,					\
 	.ctxsize	= sizeof ( struct _cbc_name ## _context ),	\
 	.blocksize	= _blocksize,					\
+	.alignsize	= _blocksize,					\
 	.authsize	= 0,						\
 	.setkey		= _cbc_name ## _setkey,				\
 	.setiv		= _cbc_name ## _setiv,				\

src/include/ipxe/crypto.h

@@ -51,8 +51,24 @@ struct cipher_algorithm {
 	const char *name;
 	/** Context size */
 	size_t ctxsize;
-	/** Block size */
+	/** Block size
+	 *
+	 * Every call to encrypt() or decrypt() must be for a multiple
+	 * of this size.
+	 */
 	size_t blocksize;
+	/** Alignment size
+	 *
+	 * Every call to encrypt() or decrypt() must begin at a
+	 * multiple of this offset from the start of the stream.
+	 * (Equivalently: all but the last call to encrypt() or
+	 * decrypt() must be for a multiple of this size.)
+	 *
+	 * For ciphers supporting additional data, the main data
+	 * stream and additional data stream are both considered to
+	 * begin at offset zero.
+	 */
+	size_t alignsize;
 	/** Authentication tag size */
 	size_t authsize;
 	/** Set key

src/include/ipxe/ecb.h

@@ -47,6 +47,7 @@ struct cipher_algorithm _ecb_cipher = {					\
 	.name		= #_ecb_name,					\
 	.ctxsize	= sizeof ( _raw_context ),			\
 	.blocksize	= _blocksize,					\
+	.alignsize	= _blocksize,					\
 	.authsize	= 0,						\
 	.setkey		= _ecb_name ## _setkey,				\
 	.setiv		= _ecb_name ## _setiv,				\

src/include/ipxe/gcm.h

@@ -121,6 +121,7 @@ struct cipher_algorithm _gcm_cipher = {					\
 	.name		= #_gcm_name,					\
 	.ctxsize	= sizeof ( struct _gcm_name ## _context ),	\
 	.blocksize	= 1,						\
+	.alignsize	= sizeof ( union gcm_block ),			\
 	.authsize	= sizeof ( union gcm_block ),			\
 	.setkey		= _gcm_name ## _setkey,				\
 	.setiv		= _gcm_name ## _setiv,				\

src/tests/cipher_test.c

@@ -131,8 +131,18 @@ void cipher_decrypt_okx ( struct cipher_test *test, const char *file,
  */
 void cipher_okx ( struct cipher_test *test, const char *file,
 		  unsigned int line ) {
+	struct cipher_algorithm *cipher = test->cipher;
+	size_t len = test->len;
 
+	/* Sanity checks */
+	okx ( cipher->blocksize != 0, file, line );
+	okx ( ( len % cipher->blocksize ) == 0, file, line );
+	okx ( ( cipher->alignsize % cipher->blocksize ) == 0, file, line );
+
+	/* Report encryption test result */
 	cipher_encrypt_okx ( test, file, line );
+
+	/* Report decryption test result */
 	cipher_decrypt_okx ( test, file, line );
 }