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Re: [libvirt] [PATCH v5 2/6] util: Introduce encryption APIs



On Thu, May 19, 2016 at 16:29:01 -0400, John Ferlan wrote:
> Introduce virCryptoHaveCipher and virCryptoEncryptData to handle
> performing encryption.
> 
>  virCryptoHaveCipher:
>    Boolean function to determine whether the requested cipher algorithm
>    is available. It's expected this API will be called prior to
>    virCryptoEncryptdata. It will return true/false.
> 
>  virCryptoEncryptData:
>    Based on the requested cipher type, call the specific encryption
>    API to encrypt the data.
> 
> Currently the only algorithm support is the AES 256 CBC encryption.
> 
> Adjust tests for the API's
> 
> Signed-off-by: John Ferlan <jferlan redhat com>
> ---
>  configure.ac             |   1 +
>  src/libvirt_private.syms |   2 +
>  src/util/vircrypto.c     | 192 ++++++++++++++++++++++++++++++++++++++++++++++-
>  src/util/vircrypto.h     |  20 ++++-
>  tests/vircryptotest.c    | 100 +++++++++++++++++++++++-
>  5 files changed, 312 insertions(+), 3 deletions(-)

[...]

> diff --git a/src/util/vircrypto.c b/src/util/vircrypto.c
> index 39a479a..b8f5554 100644
> --- a/src/util/vircrypto.c
> +++ b/src/util/vircrypto.c

[...]

> @@ -76,3 +85,184 @@ virCryptoHashString(virCryptoHash hash,
>  
>      return 0;
>  }
> +
> +
> +/* virCryptoHaveCipher:
> + * @algorithm: Specific cipher algorithm desired
> + *
> + * Expected to be called prior to virCryptoEncryptData in order
> + * to determine whether the requested encryption option is available,
> + * so that "other" alternatives can be taken if the algorithm is
> + * not available.
> + *
> + * Returns true if we can support the encryption.
> + */
> +bool
> +virCryptoHaveCipher(virCryptoCipher algorithm)
> +{
> +    switch (algorithm) {
> +
> +    case VIR_CRYPTO_CIPHER_AES256CBC:
> +#ifdef HAVE_GNUTLS_CIPHER_ENCRYPT
> +    return true;
> +#else
> +    return false;
> +#endif
> +
> +    case VIR_CRYPTO_CIPHER_NONE:
> +    case VIR_CRYPTO_CIPHER_LAST:
> +        break;
> +    };
> +
> +    return false;
> +}
> +
> +
> +#ifdef HAVE_GNUTLS_CIPHER_ENCRYPT
> +/* virCryptoEncryptDataAESgntuls:
> + *
> + * Performs the AES gnutls encryption
> + *
> + * Same input as virCryptoEncryptData, except the algoritm is replaced
> + * by the specific gnutls algorithm.
> + *
> + * Encrypts the @data buffer using the @enckey and if available the @iv
> + *
> + * Returns 0 on success with the ciphertext being filled. It is the
> + * caller's responsibility to clear and free it. Returns -1 on failure
> + * w/ error set.
> + */
> +static int
> +virCryptoEncryptDataAESgnutls(gnutls_cipher_algorithm_t gnutls_enc_alg,
> +                              uint8_t *enckey,
> +                              size_t enckeylen,
> +                              uint8_t *iv,
> +                              size_t ivlen,
> +                              uint8_t *data,
> +                              size_t datalen,
> +                              uint8_t **ciphertextret,
> +                              size_t *ciphertextlenret)
> +{
> +    int rc;
> +    size_t i;
> +    gnutls_cipher_hd_t handle = NULL;
> +    gnutls_datum_t enc_key;
> +    gnutls_datum_t iv_buf;
> +    uint8_t *ciphertext;
> +    size_t ciphertextlen;
> +
> +    /* Allocate a padded buffer, copy in the data */
> +    ciphertextlen = VIR_ROUND_UP(datalen, 16);
> +    if (VIR_ALLOC_N(ciphertext, ciphertextlen) < 0)
> +        return -1;
> +    memcpy(ciphertext, data, datalen);
> +
> +     /* Fill in the padding of the buffer with the size of the padding
> +      * which is required for decryption. */
> +    for (i = datalen; i < ciphertextlen; i++)
> +        ciphertext[i] = ciphertextlen - datalen;
> +
> +    /* Initialize the gnutls cipher */
> +    enc_key.size = enckeylen;
> +    enc_key.data = enckey;
> +    if (iv) {
> +        iv_buf.size = ivlen;
> +        iv_buf.data = iv;
> +    }
> +    if ((rc = gnutls_cipher_init(&handle, gnutls_enc_alg,
> +                                 &enc_key, &iv_buf)) < 0) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR,
> +                       _("failed to initialize cipher: '%s'"),
> +                       gnutls_strerror(rc));
> +        goto error;
> +    }
> +
> +    /* Encrypt the data and free the memory for cipher operations */
> +    rc = gnutls_cipher_encrypt(handle, ciphertext, ciphertextlen);
> +    gnutls_cipher_deinit(handle);
> +    if (rc < 0) {
> +        virReportError(VIR_ERR_INTERNAL_ERROR,
> +                       _("failed to encrypt the data: '%s'"),
> +                       gnutls_strerror(rc));
> +        goto error;
> +    }
> +
> +    *ciphertextret = ciphertext;
> +    *ciphertextlenret = ciphertextlen;
> +    return 0;
> +
> + error:
> +    VIR_DISPOSE_N(ciphertext, ciphertextlen);
> +    return -1;

In both cases you should clear the stack'd copy of the encryption key.

> +}
> +#endif
> +
> +
> +/* virCryptoEncryptData:
> + * @algorithm: algoritm desired for encryption
> + * @enckey: encryption key
> + * @enckeylen: encription key length
> + * @iv: initialization vector
> + * @ivlen: length of initialization vector
> + * @data: data to encrypt
> + * @datalen: length of data
> + * @ciphertext: stream of bytes allocated to store ciphertext
> + * @ciphertextlen: size of the stream of bytes
> + *
> + * If available, attempt and return the requested encryption type
> + * using the parameters passed.
> + *
> + * Returns 0 on success, -1 on failure with error set
> + */
> +int
> +virCryptoEncryptData(virCryptoCipher algorithm,
> +                     uint8_t *enckey,
> +                     size_t enckeylen,
> +                     uint8_t *iv,
> +                     size_t ivlen,
> +                     uint8_t *data,
> +                     size_t datalen,
> +                     uint8_t **ciphertext,
> +                     size_t *ciphertextlen)
> +{
> +    switch (algorithm) {
> +    case VIR_CRYPTO_CIPHER_AES256CBC:
> +        if (enckeylen != 32) {
> +            virReportError(VIR_ERR_INVALID_ARG,
> +                           _("AES256CBC encryption invalid keylen=%zu"),
> +                           enckeylen);
> +            return -1;
> +        }
> +
> +        if (ivlen != 16) {
> +            virReportError(VIR_ERR_INVALID_ARG,
> +                           _("AES256CBC initialization vector invalid len=%zu"),
> +                           ivlen);
> +            return -1;
> +        }
> +
> +#ifdef HAVE_GNUTLS_CIPHER_ENCRYPT
> +        /*
> +         * Encrypt the data buffer using an encryption key and
> +         * initialization vector via the gnutls_cipher_encrypt API
> +         * for GNUTLS_CIPHER_AES_256_CBC.
> +         */
> +        return virCryptoEncryptDataAESgnutls(GNUTLS_CIPHER_AES_256_CBC,
> +                                             enckey, enckeylen, iv, ivlen,
> +                                             data, datalen,
> +                                             ciphertext, ciphertextlen);
> +#else
> +        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> +                       _("no encryption algorithm exists"));

That is quite a strong message. I'd say that the chosen algorithm is not
supported.

> +        return -1;
> +#endif
> +
> +    case VIR_CRYPTO_CIPHER_NONE:
> +    case VIR_CRYPTO_CIPHER_LAST:
> +        break;
> +    }
> +
> +    virReportError(VIR_ERR_INVALID_ARG,
> +                   _("algorithm=%d is not supported"), algorithm);

e.g. as you do here.

[...]

> --- a/src/util/vircrypto.h
> +++ b/src/util/vircrypto.h

[...]

> @@ -37,4 +45,14 @@ virCryptoHashString(virCryptoHash hash,
>      ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(3)
>      ATTRIBUTE_RETURN_CHECK;
>  
> +bool virCryptoHaveCipher(virCryptoCipher algorithm);
> +
> +int virCryptoEncryptData(virCryptoCipher algorithm,
> +                         uint8_t *enckey, size_t enckeylen,
> +                         uint8_t *iv, size_t ivlen,
> +                         uint8_t *data, size_t datalen,
> +                         uint8_t **ciphertext, size_t *ciphertextlen)
> +    ATTRIBUTE_NONNULL(2) ATTRIBUTE_NONNULL(6)
> +    ATTRIBUTE_NONNULL(8) ATTRIBUTE_RETURN_CHECK;

ciphertext and ciphertextlen must be nonnull too.

> +
>  #endif /* __VIR_CRYPTO_H__ */
> diff --git a/tests/vircryptotest.c b/tests/vircryptotest.c
> index bfc47db..1d719d9 100644
> --- a/tests/vircryptotest.c
> +++ b/tests/vircryptotest.c

[...]

> @@ -56,10 +58,82 @@ testCryptoHash(const void *opaque)
>  }
>  
>  
> +struct testCryptoEncryptData {
> +    virCryptoCipher algorithm;
> +    uint8_t *input;
> +    size_t inputlen;
> +    uint8_t *ciphertext;
> +    size_t ciphertextlen;
> +};
> +
> +static int
> +testCryptoEncrypt(const void *opaque)
> +{
> +    const struct testCryptoEncryptData *data = opaque;
> +    size_t i;
> +    uint8_t *enckey = NULL;
> +    size_t enckeylen = 32;
> +    uint8_t *iv = NULL;
> +    size_t ivlen = 16;
> +    uint8_t *ciphertext = NULL;
> +    size_t ciphertextlen = 0;
> +    int ret = -1;
> +
> +    if (!virCryptoHaveCipher(data->algorithm)) {
> +        fprintf(stderr, "Invalid cipher algorithm=%d\n", data->algorithm);
> +        return -1;
> +    }
> +
> +    if (VIR_ALLOC_N(enckey, enckeylen) < 0 ||
> +        VIR_ALLOC_N(iv, ivlen) < 0)
> +        goto cleanup;
> +
> +    if (virRandomBytes(enckey, enckeylen) < 0 ||
> +        virRandomBytes(iv, ivlen) < 0)
> +        goto cleanup;
> +
> +    if (virCryptoEncryptData(data->algorithm, enckey, enckeylen, iv, ivlen,
> +                             data->input, data->inputlen,
> +                             &ciphertext, &ciphertextlen) < 0)
> +        goto cleanup;
> +
> +    if (data->ciphertextlen != ciphertextlen) {
> +        fprintf(stderr, "Expected ciphertextlen(%zu) doesn't match (%zu)\n",
> +                data->ciphertextlen, ciphertextlen);
> +        goto cleanup;
> +    }
> +
> +    if (memcmp(data->ciphertext, ciphertext, ciphertextlen)) {
> +        fprintf(stderr, "Expected ciphertext doesn't match\n");
> +        for (i = 0; i < ciphertextlen; i++) {
> +            if (data->ciphertext[i] != ciphertext[i]) {
> +                fprintf(stderr, "expected[%zu]=%x ciphertext[%zu]=%x\n",
> +                        i, data->ciphertext[i],
> +                        i, ciphertext[i]);

Last time I was pointing out that it doesn't make much sense to output
the difference whether encoded to base64 or not.

[...]

> @@ -84,7 +158,31 @@ mymain(void)
>      VIR_CRYPTO_HASH(VIR_CRYPTO_HASH_MD5, "The quick brown fox", "a2004f37730b9445670a738fa0fc9ee5");
>      VIR_CRYPTO_HASH(VIR_CRYPTO_HASH_SHA256, "The quick brown fox", "5cac4f980fedc3d3f1f99b4be3472c9b30d56523e632d151237ec9309048bda9");


>  
> +#undef VIR_CRYPTO_HASH
> +
> +#define VIR_CRYPTO_ENCRYPT(a, n, i, il, c, cl)   \
> +    do {                                         \
> +        struct testCryptoEncryptData data = {    \
> +            .algorithm = a,                      \
> +            .input = i,                          \
> +            .inputlen = il,                      \
> +            .ciphertext = c,                     \
> +            .ciphertextlen = cl,                 \
> +        };                                       \
> +        if (virtTestRun("Encrypt " n, testCryptoEncrypt, &data) < 0) \
> +            ret = -1;                                                \
> +    } while (0)
> +
> +    memset(&secretdata, 0, 8);
> +    memcpy(&secretdata, "letmein", 7);
> +
> +    VIR_CRYPTO_ENCRYPT(VIR_CRYPTO_CIPHER_AES256CBC, "aes265cbc",
> +                       secretdata, 7, expected_ciphertext, 16);
> +

This test will fail on builds without gnutls.

ACK with the nits fixed.

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