Re: [PATCH v11 18/21] crypto: Add aes-helpers file to support some AES modes

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jul 07, 2026 at 06:18:05PM +0200, Harald Freudenberger wrote:
> 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()
> 
> Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
> Reviewed-by: Finn Callies <fcallies@linux.ibm.com>
> ---
>  crypto/aes-helpers.c | 106 +++++++++++++++++++++++++++++++++++++++++++
>  crypto/meson.build   |   1 +
>  include/crypto/aes.h |  14 ++++++

This should be aes-helpers.h, to match the ases-helpers.c
file naming.

>  3 files changed, 121 insertions(+)
>  create mode 100644 crypto/aes-helpers.c
> 
> diff --git a/crypto/aes-helpers.c b/crypto/aes-helpers.c
> new file mode 100644
> index 0000000000..39ca153737
> --- /dev/null
> +++ b/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 <stdint.h>
> +#include <string.h>

Neither of these should be used, instead this should be
including qemu/osdep.h

> +#include "crypto/aes.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 litte 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);
> +}
> diff --git a/crypto/meson.build b/crypto/meson.build
> index b51597a879..675f27311c 100644
> --- a/crypto/meson.build
> +++ b/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',
> diff --git a/include/crypto/aes.h b/include/crypto/aes.h
> index 381f24c902..df6239cb9c 100644
> --- a/include/crypto/aes.h
> +++ b/include/crypto/aes.h
> @@ -37,4 +37,18 @@ AES_Td0[x] = Si[x].[0e, 09, 0d, 0b];
>  
>  extern const uint32_t AES_Te0[256], AES_Td0[256];
>  
> +void AES_xor(const unsigned char *src1, const unsigned char *src2,
> +             unsigned char *dst);
> +void AES_cbc_encrypt(const unsigned char *in, unsigned char *out,
> +                     unsigned char *iv, const AES_KEY *key);
> +void AES_cbc_decrypt(const unsigned char *in, unsigned char *out,
> +                     unsigned char *iv, const AES_KEY *key);
> +void  AES_ctr_encrypt(const unsigned char *in, unsigned char *out,
> +                      const unsigned char *ctr, const AES_KEY *key);
> +void AES_xts_prep_next_tweak(unsigned char *tweak);
> +void AES_xts_encrypt(const unsigned char *in, unsigned char *out,
> +                     const unsigned char *tweak, const AES_KEY *key);
> +void AES_xts_decrypt(const unsigned char *in, unsigned char *out,
> +                     const unsigned char *tweak, const AES_KEY *key);

Aside from putting them in aes-helpers.h can you also provide
basic API docs for them inline in the header.

With regards,
Daniel
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