In a previous PR (Fix heap corruption in implementation of truncated HMAC
extension #425) the place where MAC is computed was changed from the end of
the SSL I/O buffer to a local buffer (then (part of) the content of the local
buffer is either copied to the output buffer of compare to the input buffer).
Unfortunately, this change was made only for TLS 1.0 and later, leaving SSL
3.0 in an inconsistent state due to ssl_mac() still writing to the old,
hard-coded location, which, for MAC verification, resulted in later comparing
the end of the input buffer (containing the computed MAC) to the local buffer
(uninitialised), most likely resulting in MAC verification failure, hence no
interop (even with ourselves).
This commit completes the move to using a local buffer by using this strategy
for SSL 3.0 too. Fortunately ssl_mac() was static so it's not a problem to
change its signature.
The previous commit reduced the internal header size to 5 bytes in case of
TLS. This is not a valid since in that situation Mbed TLS internally uses the
first 8 bytes of the message buffer for the implicit record sequence number.
Fix the x509_get_subject_alt_name() function to not accept invalid
tags. The problem was that the ASN.1 class for tags consists of two
bits. Simply doing bit-wise and of the CONTEXT_SPECIFIC macro with the
input tag has the potential of accepting tag values 0x10 (private)
which would indicate that the certificate has an incorrect format.
In case truncated HMAC must be used but the Mbed TLS peer hasn't been updated
yet, one can use the compile-time option MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT to
temporarily fall back to the old, non-compliant implementation of the truncated
HMAC extension.
Add a DTLS small packet test for each of the following combinations:
- DTLS version: 1.0 or 1.2
- Encrypt then MAC extension enabled
- Truncated HMAC extension enabled
Large packets tests for DTLS are currently not possible due to parameter
constraints in ssl_server2.
This commit ensures that there is a small packet test for at least any
combination of
- SSL/TLS version: SSLv3, TLS 1.0, TLS 1.1 or TLS 1.2
- Stream cipher (RC4) or Block cipher (AES)
- Usage of Encrypt then MAC extension [TLS only]
- Usage of truncated HMAC extension [TLS only]
Noticed that the test cases in ssl-opt.sh exercising the truncated HMAC
extension do not depend on MBEDTLS_SSL_TRUNCATED_HMAC being enabled in
config.h. This commit fixes this.
The truncated HMAC extension as described in
https://tools.ietf.org/html/rfc6066.html#section-7 specifies that when truncated
HMAC is used, only the HMAC output should be truncated, while the HMAC key
generation stays unmodified. This commit fixes Mbed TLS's behavior of also
truncating the key, potentially leading to compatibility issues with peers
running other stacks than Mbed TLS.
Details:
The keys for the MAC are pieces of the keyblock that's generated from the
master secret in `mbedtls_ssl_derive_keys` through the PRF, their size being
specified as the size of the digest used for the MAC, regardless of whether
truncated HMAC is enabled or not.
/----- MD size ------\ /------- MD size ----\
Keyblock +----------------------+----------------------+------------------+---
now | MAC enc key | MAC dec key | Enc key | ...
(correct) +----------------------+----------------------+------------------+---
In the previous code, when truncated HMAC was enabled, the HMAC keys
were truncated to 10 bytes:
/-10 bytes-\ /-10 bytes-\
Keyblock +-------------+-------------+------------------+---
previously | MAC enc key | MAC dec key | Enc key | ...
(wrong) +-------------+-------------+------------------+---
The reason for this was that a single variable `transform->maclen` was used for
both the keysize and the size of the final MAC, and its value was reduced from
the MD size to 10 bytes in case truncated HMAC was negotiated.
This commit fixes this by introducing a temporary variable `mac_key_len` which
permanently holds the MD size irrespective of the presence of truncated HMAC,
and using this temporary to obtain the MAC key chunks from the keyblock.
Fix missing definition of mbedtls_zeroize when MBEDTLS_FS_IO is
disabled in the configuration.
Introduced by d08ae68237
Merge remote-tracking branch 'upstream-public/pr/1112' into mbedtls-2.1
