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Remove ciphersuite_info from ssl_transform

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Prior to this commit, the security parameter struct `ssl_transform`
contained a `ciphersuite_info` field pointing to the information
structure for the negotiated ciphersuite. However, the only
information extracted from that structure that was used in the core
encryption and decryption functions `ssl_encrypt_buf`/`ssl_decrypt_buf`
was the authentication tag length in case of an AEAD cipher.

The present commit removes the `ciphersuite_info` field from the
`ssl_transform` structure and adds an explicit `taglen` field
for AEAD authentication tag length.

This is in accordance with the principle that the `ssl_transform`
structure should contain the raw parameters needed for the record
encryption and decryption functions to work, but not the higher-level
information that gave rise to them. For example, the `ssl_transform`
structure implicitly contains the encryption/decryption keys within
their cipher contexts, but it doesn't contain the SSL master or
premaster secrets. Likewise, it contains an explicit `maclen`, while
the status of the 'Truncated HMAC' extension -- which  determines the
value of `maclen` when the `ssl_transform` structure is created in
`ssl_derive_keys` -- is not contained in `ssl_transform`.

The `ciphersuite_info` pointer was used in other places outside
the encryption/decryption functions during the handshake, and for
these functions to work, this commit adds a `ciphersuite_info` pointer
field to the handshake-local `ssl_handshake_params` structure.
This commit is contained in:
Hanno Becker 2017-12-27 21:34:08 +00:00
parent 88aaf652b1
commit e694c3ef3e
4 changed files with 61 additions and 63 deletions
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7
include/mbedtls/ssl_internal.h
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@ -420,6 +420,8 @@ struct mbedtls_ssl_handshake_params
const unsigned char *, size_t,
unsigned char *, size_t);
mbedtls_ssl_ciphersuite_t const *ciphersuite_info;
size_t pmslen; /*!< premaster length */
unsigned char randbytes[64]; /*!< random bytes */
@ -463,12 +465,11 @@ struct mbedtls_ssl_transform
/*
* Session specific crypto layer
*/
const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
/*!< Chosen cipersuite_info */
size_t minlen; /*!< min. ciphertext length */
size_t ivlen; /*!< IV length */
size_t fixed_ivlen; /*!< Fixed part of IV (AEAD) */
size_t maclen; /*!< MAC length */
size_t maclen; /*!< MAC(CBC) len */
size_t taglen; /*!< TAG(AEAD) len */
unsigned char iv_enc[16]; /*!< IV (encryption) */
unsigned char iv_dec[16]; /*!< IV (decryption) */