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chachapoly: warn against piecewise decryption

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Manuel Pégourié-Gonnard 2018-05-24 19:33:59 +02:00
parent f4f01b6b7a
commit be78b07015
1 changed files with 32 additions and 2 deletions
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34
include/mbedtls/chachapoly.h
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@ -89,13 +89,31 @@ mbedtls_chachapoly_context;
* \c mbedtls_chachapoly_crypt_and_tag() or
* \c mbedtls_chachapoly_auth_decrypt().
*
* In order to encrypt or decrypt messages piecewise, for each
* In order to encrypt messages piecewise, for each
* message you should make a call to
* \c mbedtls_chachapoly_starts(), then 0 or more calls to
* \c mbedtls_chachapoly_update_aad(), then 0 or more calls to
* \c mbedtls_chachapoly_update(), then one call to
* \c mbedtls_chachapoly_finish().
*
* \warning Decryption with the piecewise API is discouraged! Always
* use \c mbedtls_chachapoly_auth_decrypt() when possible!
*
* If however this is not possible because the data is too
* large to fit in memory, you need to:
*
* - call \c mbedtls_chachapoly_starts() and (if needed)
* \c mbedtls_chachapoly_update_aad() as above,
* - call \c mbedtls_chachapoly_update() multiple times and
* ensure its output (the plaintext) is NOT used in any other
* way than placing it in temporary storage at this point,
* - call \c mbedtls_chachapoly_finish() to compute the
* authentication tag and compared it in constant time to the
* tag received with the ciphertext.
*
* If the tags are not equal, you must immediately discard
* all previous outputs of \c mbedtls_chachapoly_update(),
* otherwise you can now safely use the plaintext.
*
* \param ctx The ChachaPoly context to initialize.
*/
@ -134,10 +152,13 @@ int mbedtls_chachapoly_setkey( mbedtls_chachapoly_context *ctx,
* \note If the context is being used for AAD only (no data to
* encrypt or decrypt) then \p mode can be set to any value.
*
* \warning Decryption with the piecewise API is discouraged, see the
* warning on \c mbedtls_chachapoly_init().
*
* \param ctx The ChaCha20-Poly1305 context.
* \param nonce The nonce/IV to use for the message. Must be 12 bytes.
* \param mode The operation to perform: #MBEDTLS_CHACHAPOLY_ENCRYPT or
* #MBEDTLS_CHACHAPOLY_DECRYPT.
* #MBEDTLS_CHACHAPOLY_DECRYPT (discouraged, see warning).
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_POLY1305_BAD_INPUT_DATA
@ -169,6 +190,9 @@ int mbedtls_chachapoly_starts( mbedtls_chachapoly_context *ctx,
* been processed by \c mbedtls_chachapoly_update(),
* or if the context has been finished.
*
* \warning Decryption with the piecewise API is discouraged, see the
* warning on \c mbedtls_chachapoly_init().
*
* \param ctx The ChaCha20-Poly1305 context to use.
* \param aad_len The length (in bytes) of the AAD. The length has no
* restrictions.
@ -200,6 +224,9 @@ int mbedtls_chachapoly_update_aad( mbedtls_chachapoly_context *ctx,
* this function 0 times, if no data is to be encrypted
* or decrypted.
*
* \warning Decryption with the piecewise API is discouraged, see the
* warning on \c mbedtls_chachapoly_init().
*
* \param ctx The ChaCha20-Poly1305 context to use.
* \param len The length (in bytes) of the data to encrypt or decrypt.
* \param input The buffer containing the data to encrypt or decrypt.
@ -227,6 +254,9 @@ int mbedtls_chachapoly_update( mbedtls_chachapoly_context *ctx,
* \param ctx The ChaCha20-Poly1305 context to use.
* \param mac The buffer to where the 128-bit (16 bytes) MAC is written.
*
* \warning Decryption with the piecewise API is discouraged, see the
* warning on \c mbedtls_chachapoly_init().
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_POLY1305_BAD_INPUT_DATA
* if \p ctx or \p mac are NULL.