We generate material for both MSK and EMSK even though we only need the
former. Because HKDF-Expand-Label(), on which the export functionality
is based, encodes the requested key length, we have to allocate the same
number of bytes as e.g. FreeRADIUS does (i.e. if we only request 64
bytes, those won't be the same as the first 64 bytes after requesting
128 bytes).
Unfortunately, key derivation for TLS-based methods is currently not
standardized for TLS 1.3. There is a draft [1], which defines a scheme
that's different from previous versions (instead of individual label
strings it uses a single one and passes the EAP type/code as context
value to TLS-Export()). The current code is compatible to FreeRADIUS
3.0.x, which doesn't implement it according to that draft yet (there are
unreleased changes for EAP-TLS, not for the other methods, but these only
switch the label, no context value is passed). In a separate draft
for EAP-TLS [2] there is an altogether different scheme defined in the
latest version (label combined with EAP method, no context and separate
derivation for MSK and EMSK).
So this is a mess and we will have to change this later with the inevitable
compatibility issues (we should definitely disable TLS 1.3 by default).
[1] https://tools.ietf.org/html/draft-ietf-emu-tls-eap-types
[2] https://tools.ietf.org/html/draft-ietf-emu-eap-tls13
PKCS#1 v1.5 signatures are not defined for use with TLS 1.3 (they can
only appear in certificates, we now send a signature_algorithms_cert
extension to indicate support for them). So for RSA certificates, we
must support RSA-PSS signatures.
There are two sets of schemes, that are differentiated by the type of
RSA key used for the signature, one is for classic RSA keys (rsaEncryption
OID), which can also be used with PKCS#1 when using TLS 1.2, the other
is for RSA-PSS keys (RSASSA-PSS OID), which are not yet commonly
used (and can't be generated by our pki tool). According to the RFC,
PSS must also be supported for TLS 1.2 if the schemes are included in
the signature_algorithms extension (e.g. OpenSSL does not use PKCS#1 v1.5
anymore if PSS is proposed).
This changes how these schemes are stored and enumerated (they are not
treated as combination of hash algo and key type anymore).
Legacy schemes (MD5/SHA-1) are removed.
With the previous code, there was an issue when replying to TLS 1.3
post-handshake messages. In this case, SUCCESS is eventually returned
from build(), however, no actual data has been received so in_done is 0.
This was interpreted as EOF, plain_eof was set to TRUE and no further data
was read from the socket afterwards.
Returning SUCCESS from build() if the exchange is initiated by
write_(), as is the case with the finished reply, never was a problem
because there the return value of 0 is not interpreted as EOF.
If data is processed that eventually includes a TLS close notify, build()
will fail after a close notify has been sent in turn. However, propagating
that error immediately when reading prevented ever returning the data
already processed before the close notify was received.
Note that this breaks connecting to many TLS 1.3 servers until we support
HelloRetryRequest as we now send a key_share for ECP_256 while still
proposing other groups, so many servers request to use CURVE_25519.
These DH groups don't use the point format prefix (RFC 8422 deprecated
any other format anyway). Since they are enumerated now, they can also
be used by servers for TLS 1.2.
There is no point proposing legacy (or future) cipher suites depending on
the proposed TLS versions. It was actually possible to negotiate and use
cipher suites only defined for TLS 1.2 with earlier TLS versions.
The code is a minimal handshake with the HelloRetryRequest message
implementation missing.
Can be tested with an OpenSSL server running TLS 1.3. The server must
be at least version 1.1.1 (September 2018).
Co-authored-by: ryru <pascal.knecht@hsr.ch>
TLS 1.3 uses HMAC-based Extract-and-Expand Key Derivation Function (HKDF)
as defined in RFC 5869 to compute traffic secrets.
Co-authored-by: bytinbit <meline.sieber@hsr.ch>
The key material, in particular the nonce/IV, is derived differently and
the IV is also generated in a different way. Additionally, the actual
content type is encrypted and there may be optional padding to mask the
actual size of the encrypted data.
Tobias Brunner