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Correct and clarify the documentation of GCM whole-message functions

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Clarify the roles of the buffer parameter and their sizes.

Remove a statement about input size restrictions that only applies to
mbedtls_gcm_update, not to the whole-message functions.

Document the possible error codes.

Warn that mbedtls_gcm_crypt_and_tag in decrypt mode does not
authenticate the data and recommend using mbedtls_gcm_auth_decrypt
instead.
This commit is contained in:
Gilles Peskine 2018-06-01 17:55:41 +02:00
parent 2f3a581567
commit 80f679b938
1 changed files with 32 additions and 14 deletions
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44
include/mbedtls/gcm.h
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@ -113,21 +113,35 @@ int mbedtls_gcm_setkey( mbedtls_gcm_context *ctx,
* the same as input buffer. If the buffers overlap, the output
* buffer must trail at least 8 Bytes behind the input buffer.
*
* \warning When this function performs a decryption, it outputs the
* authentication tag and does not verify that the data is
* authentic. You should use this function to perform encryption
* only. For decryption, use mbedtls_gcm_auth_decrypt() instead.
*
* \param ctx The GCM context to use for encryption or decryption.
* \param mode The operation to perform: #MBEDTLS_GCM_ENCRYPT or
* #MBEDTLS_GCM_DECRYPT.
* \param length The length of the input data. This must be a multiple of
* 16 except in the last call before mbedtls_gcm_finish().
* #MBEDTLS_GCM_DECRYPT. Note that during decryption, the
* tag is not verified. You should use this function only
* to encrypt data, and use mbedtls_gcm_auth_decrypt()
* to decrypt.
* \param length The length of the input data, which is equal to the length
* of the output data.
* \param iv The initialization vector.
* \param iv_len The length of the IV.
* \param add The buffer holding the additional data.
* \param add_len The length of the additional data.
* \param input The buffer holding the input data.
* \param output The buffer for holding the output data.
* \param input The buffer holding the input data. Its size is \b length.
* \param output The buffer for holding the output data. It must have room
* for \b length bytes.
* \param tag_len The length of the tag to generate.
* \param tag The buffer for holding the tag.
*
* \return \c 0 on success.
* \return \c 0 if the encryption or decryption was performed
* successfully. Note that in #MBEDTLS_GCM_DECRYPT mode,
* this does not indicate that the data is authentic.
* \return #MBEDTLS_ERR_GCM_BAD_INPUT if the lengths are not valid.
* \return #MBEDTLS_ERR_GCM_HW_ACCEL_FAILED or a cipher-specific
* error code if the encryption or decryption failed.
*/
int mbedtls_gcm_crypt_and_tag( mbedtls_gcm_context *ctx,
int mode,
@ -150,19 +164,23 @@ int mbedtls_gcm_crypt_and_tag( mbedtls_gcm_context *ctx,
* must trail at least 8 Bytes behind the input buffer.
*
* \param ctx The GCM context.
* \param length The length of the input data. This must be a multiple
* of 16 except in the last call before mbedtls_gcm_finish().
* \param length The length of the ciphertext to decrypt, which is also
* the length of the decrypted plaintext.
* \param iv The initialization vector.
* \param iv_len The length of the IV.
* \param add The buffer holding the additional data.
* \param add_len The length of the additional data.
* \param tag The buffer holding the tag.
* \param tag_len The length of the tag.
* \param input The buffer holding the input data.
* \param output The buffer for holding the output data.
* \param tag The buffer holding the tag to verify.
* \param tag_len The length of the tag to verify.
* \param input The buffer holding the ciphertext. Its size is \b length.
* \param output The buffer for holding the decrypted plaintext. It must
* have room for \b length bytes.
*
* \return 0 if successful and authenticated.
* \return \c 0 if successful and authenticated.
* \return #MBEDTLS_ERR_GCM_AUTH_FAILED if the tag does not match.
* \return #MBEDTLS_ERR_GCM_BAD_INPUT if the lengths are not valid.
* \return #MBEDTLS_ERR_GCM_HW_ACCEL_FAILED or a cipher-specific
* error code if the decryption failed.
*/
int mbedtls_gcm_auth_decrypt( mbedtls_gcm_context *ctx,
size_t length,