crypto: Add aes-helpers file to support some AES modes

Add a new file crypto/aes-helpers.c with simple functions
to support some AES modes:
- AES cbc: AES_cbc_encrypt() AES_cbc_decrypt()
- AES ctr: AES_ctr_encrypt()
- AES xts: AES_xts_encrypt() AES_xts_decrypt()
and some AES related helpers:
- AES_xor()
- AES_xts_prep_next_tweak()
Add header file include/crypto/aes-helpers.h for these functions

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Finn Callies <fcallies@linux.ibm.com>
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260824083204.40877-8-freude@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>

crypto/aes-helpers.c

@@ -0,0 +1,106 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * AES helper functions and mode implementations
+ *
+ * Authors:
+ *   Harald Freudenberger <freude@linux.ibm.com>
+ */
+
+#include "qemu/osdep.h"
+#include "crypto/aes.h"
+#include "crypto/aes-helpers.h"
+
+void AES_xor(const unsigned char *src1, const unsigned char *src2,
+             unsigned char *dst)
+{
+    int i;
+
+    for (i = 0; i < AES_BLOCK_SIZE; i++) {
+        dst[i] = src1[i] ^ src2[i];
+    }
+}
+
+void AES_cbc_encrypt(const unsigned char *in, unsigned char *out,
+                     unsigned char *iv, const AES_KEY *key)
+{
+    unsigned char buf[AES_BLOCK_SIZE];
+
+    /* in xor iv => buf */
+    AES_xor(in, iv, buf);
+    /* encrypt buf => out */
+    AES_encrypt(buf, out, key);
+    /* prep iv for next round */
+    memcpy(iv, out, AES_BLOCK_SIZE);
+}
+
+void AES_cbc_decrypt(const unsigned char *in, unsigned char *out,
+                     unsigned char *iv, const AES_KEY *key)
+{
+    unsigned char buf[AES_BLOCK_SIZE];
+
+    /* decrypt in => buf */
+    AES_decrypt(in, buf, key);
+    /* buf xor iv => out */
+    AES_xor(buf, iv, out);
+    /* prep iv for next round */
+    memcpy(iv, in, AES_BLOCK_SIZE);
+}
+
+void AES_ctr_encrypt(const unsigned char *in, unsigned char *out,
+                     const unsigned char *ctr, const AES_KEY *key)
+{
+    unsigned char buf[AES_BLOCK_SIZE];
+
+    /* encrypt ctr => buf */
+    AES_encrypt(ctr, buf, key);
+    /* exor input data with encrypted ctr => out */
+    AES_xor(in, buf, out);
+}
+
+/*
+ * Tweak calculation for AES XTS.
+ * Multiply tweak by α (x) in GF(2^128) per IEEE 1619-2007. The tweak
+ * is a 128-bit little-endian integer (tweak[0]=LSB, tweak[15]=MSB).
+ * This implementation has been verified on little and big endian.
+ */
+void AES_xts_prep_next_tweak(unsigned char *tweak)
+{
+    unsigned char carry;
+    int i;
+
+    carry = tweak[AES_BLOCK_SIZE - 1] >> 7;
+
+    for (i = AES_BLOCK_SIZE - 1; i > 0; i--) {
+        tweak[i] = (unsigned char)((tweak[i] << 1) | (tweak[i - 1] >> 7));
+    }
+
+    tweak[i] = (unsigned char)(tweak[i] << 1);
+    tweak[i] ^= (unsigned char)(0x87 & (unsigned char)(-(unsigned char)carry));
+}
+
+void AES_xts_encrypt(const unsigned char *in, unsigned char *out,
+                     const unsigned char *tweak, const AES_KEY *key)
+{
+    unsigned char buf1[AES_BLOCK_SIZE], buf2[AES_BLOCK_SIZE];
+
+    /* in xor tweak => buf1 */
+    AES_xor(in, tweak, buf1);
+    /* encrypt buf1 => buf2 */
+    AES_encrypt(buf1, buf2, key);
+    /* buf2 xor tweak => out */
+    AES_xor(buf2, tweak, out);
+}
+
+void AES_xts_decrypt(const unsigned char *in, unsigned char *out,
+                     const unsigned char *tweak, const AES_KEY *key)
+{
+    unsigned char buf1[AES_BLOCK_SIZE], buf2[AES_BLOCK_SIZE];
+
+    /* in xor tweak => buf1 */
+    AES_xor(in, tweak, buf1);
+    /* encrypt buf1 => buf2 */
+    AES_decrypt(buf1, buf2, key);
+    /* buf2 xor tweak => out */
+    AES_xor(buf2, tweak, out);
+}

crypto/meson.build

@@ -55,6 +55,7 @@ system_ss.add(when: gnutls, if_true: files('tls-cipher-suites.c'))
 
 util_ss.add(files(
   'aes.c',
+  'aes-helpers.c',
   'clmul.c',
   'init.c',
   'sm4.c',

include/crypto/aes-helpers.h

@@ -0,0 +1,109 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ *
+ * AES helper functions and modes
+ */
+
+#ifndef QEMU_AES_HELPERS_H
+#define QEMU_AES_HELPERS_H
+
+/**
+ * AES_xor:
+ * @src1: first source buffer of AES_BLOCK_SIZE bytes
+ * @src2: second source buffer of AES_BLOCK_SIZE bytes
+ * @dst: destination buffer of AES_BLOCK_SIZE bytes
+ *
+ * Bitwise XOR operation between two AES blocks.
+ */
+void AES_xor(const unsigned char *src1, const unsigned char *src2,
+             unsigned char *dst);
+
+/**
+ * AES_cbc_encrypt:
+ * @in: input plaintext block of AES_BLOCK_SIZE bytes
+ * @out: output ciphertext block of AES_BLOCK_SIZE bytes
+ * @iv: IV, updated after processing for chaining
+ * @key: AES key
+ *
+ * Single block AES encrypt in CBC (Cipher Block Chaining) mode.
+ * The input block is XORed with the IV, then encrypted with AES.
+ * IV is updated at the end and is prepared for the next invocation.
+ */
+void AES_cbc_encrypt(const unsigned char *in, unsigned char *out,
+                     unsigned char *iv, const AES_KEY *key);
+
+/**
+ * AES_cbc_decrypt:
+ * @in: input ciphertext block of AES_BLOCK_SIZE bytes
+ * @out: output plaintext block of AES_BLOCK_SIZE bytes
+ * @iv: initialization vector, updated to input block for chaining
+ * @key: AES key
+ *
+ * Single block AES decrypt in CBC (Cipher Block Chaining) mode.
+ * The input block is decrypted, then XORed with the IV.
+ * IV is updated at the end and is prepared for the next invocation.
+ */
+void AES_cbc_decrypt(const unsigned char *in, unsigned char *out,
+                     unsigned char *iv, const AES_KEY *key);
+
+/**
+ * AES_ctr_encrypt:
+ * @in: input data block of AES_BLOCK_SIZE bytes
+ * @out: output data block of AES_BLOCK_SIZE bytes
+ * @ctr: counter value of AES_BLOCK_SIZE bytes
+ * @key: AES key
+ *
+ * Single block AES encrypt/decrypt in CTR (Counter) mode.
+ * The counter block is encrypted, then XORed with the
+ * input data block.
+ * In CTR mode encrypt and decrypt are identical operations.
+ * Note that the caller is responsible for incrementing the
+ * counter block.
+ */
+void  AES_ctr_encrypt(const unsigned char *in, unsigned char *out,
+                      const unsigned char *ctr, const AES_KEY *key);
+
+/**
+ * AES_xts_prep_next_tweak:
+ * @tweak: pointer to tweak value to be updated (16 bytes buffer
+ *         containing a 128 bit little endian integer)
+ *
+ * Tweak calculation for AES XTS.
+ * Prepares the next tweak value for AES-XTS mode by multiplying
+ * the current tweak by α (x) in GF(2^128) according to IEEE 1619-2007.
+ */
+void AES_xts_prep_next_tweak(unsigned char *tweak);
+
+/**
+ * AES_xts_encrypt:
+ * @in: input plaintext block of AES_BLOCK_SIZE bytes
+ * @out: output ciphertext block of AES_BLOCK_SIZE bytes
+ * @tweak: tweak value (16 bytes)
+ * @key: AES key
+ *
+ * Single block AES encrypt in XTS mode.
+ * The input is XORed with the tweak, encrypted, then XORed with
+ * the tweak again to produce the output.
+ * Note that the caller is responsible for managing the tweak value.
+ * Use AES_xts_prep_next_tweak() to advance the tweak for the next block.
+ */
+void AES_xts_encrypt(const unsigned char *in, unsigned char *out,
+                     const unsigned char *tweak, const AES_KEY *key);
+
+/**
+ * AES_xts_decrypt:
+ * @in: input ciphertext block of AES_BLOCK_SIZE bytes
+ * @out: output plaintext block of AES_BLOCK_SIZE bytes
+ * @tweak: tweak value (16 bytes)
+ * @key: AES key
+ *
+ * Single block AES decrypt in XTS mode.
+ * The input is XORed with the tweak, decrypted, then XORed with
+ * the tweak again to produce the output.
+ * Note that the caller is responsible for managing the tweak value.
+ * Use AES_xts_prep_next_tweak() to advance the tweak for the next block.
+ */
+void AES_xts_decrypt(const unsigned char *in, unsigned char *out,
+                     const unsigned char *tweak, const AES_KEY *key);
+
+#endif