Re: [PATCH v1 09/15] crypto/cipher-gcrypt: Implement AES-GCM

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

On Tue, Jul 14, 2026 at 07:29:14AM +0000, Jamin Lin wrote:
> Map QCRYPTO_CIPHER_MODE_GCM to GCRY_CIPHER_MODE_GCM and advertise it in
> qcrypto_cipher_supports() for 128-bit block ciphers. Add a GCM driver
> whose setiv accepts the (typically 96-bit) nonce, whose encrypt/decrypt
> do not require block-aligned lengths, and which implements setaad via
> gcry_cipher_authenticate() and gettag via gcry_cipher_gettag().
> 
> Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
> ---
>  crypto/cipher-gcrypt.c.inc | 101 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 101 insertions(+)
> 
> diff --git a/crypto/cipher-gcrypt.c.inc b/crypto/cipher-gcrypt.c.inc
> index 12eb9ddb5a..fce09a3c77 100644
> --- a/crypto/cipher-gcrypt.c.inc
> +++ b/crypto/cipher-gcrypt.c.inc
> @@ -65,6 +65,8 @@ static int qcrypto_cipher_mode_to_gcry_mode(QCryptoCipherMode mode)
>          return GCRY_CIPHER_MODE_CBC;
>      case QCRYPTO_CIPHER_MODE_CTR:
>          return GCRY_CIPHER_MODE_CTR;
> +    case QCRYPTO_CIPHER_MODE_GCM:
> +        return GCRY_CIPHER_MODE_GCM;
>      default:
>          return GCRY_CIPHER_MODE_NONE;
>      }
> @@ -104,6 +106,10 @@ bool qcrypto_cipher_supports(QCryptoCipherAlgo alg,
>      case QCRYPTO_CIPHER_MODE_XTS:
>      case QCRYPTO_CIPHER_MODE_CTR:
>          return true;
> +    case QCRYPTO_CIPHER_MODE_GCM:
> +        /* GCM requires a 128-bit block cipher. */
> +        return gcry_cipher_get_algo_blklen(
> +                   qcrypto_cipher_alg_to_gcry_alg(alg)) == 16;
>      default:
>          return false;
>      }
> @@ -228,6 +234,99 @@ static const struct QCryptoCipherDriver qcrypto_gcrypt_ctr_driver = {
>      .cipher_free = qcrypto_gcrypt_ctx_free,
>  };
>  
> +/*
> + * GCM is an AEAD stream mode: the IV/nonce need not match the block size,
> + * the message length need not be a multiple of the block size, associated
> + * data is fed with gcry_cipher_authenticate() and the authentication tag is
> + * read back with gcry_cipher_gettag().
> + */
> +static int qcrypto_gcrypt_gcm_setiv(QCryptoCipher *cipher,
> +                                    const uint8_t *iv, size_t niv,
> +                                    Error **errp)
> +{
> +    QCryptoCipherGcrypt *ctx = container_of(cipher, QCryptoCipherGcrypt, base);
> +    gcry_error_t err;
> +
> +    gcry_cipher_reset(ctx->handle);
> +    err = gcry_cipher_setiv(ctx->handle, iv, niv);
> +    if (err != 0) {
> +        error_setg(errp, "Cannot set IV: %s", gcry_strerror(err));
> +        return -1;
> +    }
> +
> +    return 0;
> +}
>
> +static int qcrypto_gcrypt_gcm_encrypt(QCryptoCipher *cipher, const void *in,
> +                                      void *out, size_t len, Error **errp)
> +{
> +    QCryptoCipherGcrypt *ctx = container_of(cipher, QCryptoCipherGcrypt, base);
> +    gcry_error_t err;
> +
> +    err = gcry_cipher_encrypt(ctx->handle, out, len, in, len);
> +    if (err != 0) {
> +        error_setg(errp, "Cannot encrypt data: %s", gcry_strerror(err));
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int qcrypto_gcrypt_gcm_decrypt(QCryptoCipher *cipher, const void *in,
> +                                      void *out, size_t len, Error **errp)
> +{
> +    QCryptoCipherGcrypt *ctx = container_of(cipher, QCryptoCipherGcrypt, base);
> +    gcry_error_t err;
> +
> +    err = gcry_cipher_decrypt(ctx->handle, out, len, in, len);
> +    if (err != 0) {
> +        error_setg(errp, "Cannot decrypt data: %s", gcry_strerror(err));
> +        return -1;
> +    }
> +
> +    return 0;
> +}

Is there a reason you can't use the common qcrypto_gcrypt_setiv,
qcrypto_gcrypt_decrypt and qcrypto_gcrypt_encrypt methods ?

> +
> +static int qcrypto_gcrypt_gcm_gettag(QCryptoCipher *cipher,
> +                                     uint8_t *tag, size_t len, Error **errp)
> +{
> +    QCryptoCipherGcrypt *ctx = container_of(cipher, QCryptoCipherGcrypt, base);
> +    gcry_error_t err;
> +
> +    err = gcry_cipher_gettag(ctx->handle, tag, len);
> +    if (err != 0) {
> +        error_setg(errp, "Cannot get tag: %s", gcry_strerror(err));
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static const struct QCryptoCipherDriver qcrypto_gcrypt_gcm_driver = {
> +    .cipher_encrypt = qcrypto_gcrypt_gcm_encrypt,
> +    .cipher_decrypt = qcrypto_gcrypt_gcm_decrypt,
> +    .cipher_setiv = qcrypto_gcrypt_gcm_setiv,
> +    .cipher_setaad = qcrypto_gcrypt_gcm_setaad,
> +    .cipher_gettag = qcrypto_gcrypt_gcm_gettag,
> +    .cipher_free = qcrypto_gcrypt_ctx_free,
> +};
> +
>  static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgo alg,
>                                               QCryptoCipherMode mode,
>                                               const uint8_t *key,
> @@ -259,6 +358,8 @@ static QCryptoCipher *qcrypto_cipher_ctx_new(QCryptoCipherAlgo alg,
>  
>      if (mode == QCRYPTO_CIPHER_MODE_CTR) {
>          drv = &qcrypto_gcrypt_ctr_driver;
> +    } else if (mode == QCRYPTO_CIPHER_MODE_GCM) {
> +        drv = &qcrypto_gcrypt_gcm_driver;
>      } else {
>          drv = &qcrypto_gcrypt_driver;
>      }
> -- 
> 2.43.0
> 
> 

With regards,
Daniel
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