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Add output length parameters to mbedtls_gcm_update

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Alternative implementations of GCM may delay the output of partial
blocks from mbedtls_gcm_update(). Add an output length parameter to
mbedtls_gcm_update() to allow such implementations to delay the output
of partial blocks. With the software implementation, there is no such
delay.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-04-15 17:22:35 +02:00
parent 9461e45a17
commit a56c448636
5 changed files with 112 additions and 55 deletions
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42
include/mbedtls/gcm.h
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@ -253,22 +253,42 @@ int mbedtls_gcm_starts( mbedtls_gcm_context *ctx,
* input buffer. If the buffers overlap, the output buffer
* must trail at least 8 Bytes behind the input buffer.
*
* \param ctx The GCM context. This must be initialized.
* \param length The length of the input data.
* \param input The buffer holding the input data. If \p length is greater
* than zero, this must be a readable buffer of at least that
* size in Bytes.
* \param output The buffer for holding the output data. If \p length is
* greater than zero, this must be a writable buffer of at
* least that size in Bytes.
* \param ctx The GCM context. This must be initialized.
* \param input The buffer holding the input data. If \p input_length
* is greater than zero, this must be a readable buffer
* of at least \p input_length bytes.
* \param input_length The length of the input data in bytes.
* \param output The buffer for the output data. If \p output_length
* is greater than zero, this must be a writable buffer of
* of at least \p output_size bytes.
* This function may withhold the end of the output if
* it is a partial block for the underlying block cipher.
* That is, if the cumulated input passed to
* mbedtls_gcm_update() so far (including the current call)
* is 16 *n* + *p* with *p* < 16, this function may
* withhold the last *p* bytes, which will be output by
* a subsequent call to mbedtls_gcm_update() or
* mbedtls_gcm_finish().
* \param output_size The size of the output buffer in bytes.
* This must be at least \p input_length plus the length
* of the input withheld by the previous call to
* mbedtls_gcm_update(). Therefore:
* - With arbitrary inputs, \p output_size may need to
* be as large as `input_length + 15`.
* - If all input lengths are a multiple of 16, then
* \p output_size = \p input_length is sufficient.
* \param output_length On success, \p *output_length contains the actual
* length of the output written in \p output.
* On failure, the content of \p *output_length is
* unspecified.
*
* \return \c 0 on success.
* \return #MBEDTLS_ERR_GCM_BAD_INPUT on failure.
*/
int mbedtls_gcm_update( mbedtls_gcm_context *ctx,
size_t length,
const unsigned char *input,
unsigned char *output );
const unsigned char *input, size_t input_length,
unsigned char *output, size_t output_size,
size_t *output_length );
/**
* \brief This function finishes the GCM operation and generates