Most protocols extracting keys from TLS use RFC 5705 exporters which is
commonly implemented in TLS libraries. This is the mechanism used by
EAP-TLS. (EAP-TLS actually predates RFC 5705, but RFC 5705 was defined
to be compatible with it.)
EAP-FAST, however, uses a legacy mechanism. It reuses the TLS internal
key block derivation and derives key material after the key block. This
is uncommon and a misuse of TLS internals, so not all TLS libraries
support this. Instead, we reimplement the PRF for the OpenSSL backend
and don't support it at all in the GnuTLS one.
Since these two are very different operations, split
tls_connection_prf() in two. tls_connection_export_key() implements the
standard RFC 5705 mechanism that we expect most TLS libraries to
support. tls_connection_get_eap_fast_key() implements the
EAP-FAST-specific legacy mechanism which may not be implemented on all
backends but is only used by EAP-FAST.
Signed-Off-By: David Benjamin <davidben@google.com>
This function exposes internal state of the TLS negotiated parameters
for the sole purpose of being able to implement PRF for EAP-FAST. Since
tls_connection_prf() is now taking care of all TLS-based key derivation
cases, it is cleaner to keep this detail internal to each tls_*.c
wrapper implementation.
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
tls_openssl.c is the only remaining TLS/crypto wrapper that needs the
internal PRF implementation for EAP-FAST (since
SSL_export_keying_material() is not available in older versions and does
not support server-random-before-client case). As such, it is cleaner to
assume that TLS libraries support tls_connection_prf() and move the
additional support code for the otherwise unsupported cases into
tls_openssl.c.
Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Use size_t instead of int for storing and comparing the TLV length
against the remaining buffer length to make this easier for static
analyzers to understand.
Signed-off-by: Jouni Malinen <j@w1.fi>
Prepare for multiple TLS PRF functions by renaming the SHA1+MD5 based
TLS PRF function to more specific name and add tls_prf() within the
internal TLS implementation as a wrapper for this for now.
Signed-hostap: Jouni Malinen <j@w1.fi>
In addition, start ordering header file includes to be in more
consistent order: system header files, src/utils, src/*, same
directory as the *.c file.
Jouni Malinen