Picotls is a TLS 1.3 (RFC 8446) protocol stack written in C, with the following features:
- support for three crypto engines
- "OpenSSL" backend using libcrypto for crypto and X.509 operations
- "minicrypto" backend using cifra for most crypto and micro-ecc for secp256r1
- "fusion" AES-GCM engine, optimized for QUIC and other protocols that use short AEAD blocks
- libaegis for the AEGIS AEADs
- support for PSK, PSK-DHE resumption using 0-RTT
- API for dealing directly with TLS handshake messages (essential for QUIC)
- supported extensions:
- RFC 7250 (raw public keys)
- RFC 8879 (certificate compression)
- Encrypted Client Hello (wg-draft-15)
picotls is designed to be fast, tiny, and low-latency, with the primary user being the H2O HTTP/2 server for serving HTTP/1, HTTP/2, and HTTP/3 over QUIC.
The TLS protocol implementation of picotls is licensed under the MIT license.
License and the cryptographic algorithms supported by the crypto bindings are as follows:
| Binding | License | Key Exchange | Certificate | AEAD cipher |
|---|---|---|---|---|
| minicrypto | CC0 / 2-clause BSD | secp256r1, x25519 | ECDSA (secp256r1)1 | AES-128-GCM, chacha20-poly1305, AEGIS-128L (using libaegis), AEGIS-256 (using libaegis) |
| OpenSSL | OpenSSL | secp256r1, secp384r1, secp521r1, x25519 | RSA, ECDSA (secp256r1, secp384r1, secp521r1), ed25519 | AES-128-GCM, AES-256-GCM, chacha20-poly1305, AEGIS-128L (using libaegis), AEGIS-256 (using libaegis) |
Note 1: Minicrypto binding is capable of signing a handshake using the certificate's key, but cannot verify a signature sent by the peer.
If you have cloned picotls from git then ensure that you have initialised the submodules:
% git submodule init
% git submodule update
Build using cmake:
% cmake .
% make
% make check
A dedicated documentation for using picotls with Visual Studio can be found in WindowsPort.md.
Developer documentation should be available on the wiki.
Run the test server (at 127.0.0.1:8443):
% ./cli -c /path/to/certificate.pem -k /path/to/private-key.pem 127.0.0.1 8443
Connect to the test server:
% ./cli 127.0.0.1 8443
Using resumption:
% ./cli -s session-file 127.0.0.1 8443
The session-file is read-write. The cli server implements a single-entry session cache. The cli server sends NewSessionTicket when it first sends application data after receiving ClientFinished.
Using early-data:
% ./cli -s session-file -e 127.0.0.1 8443
When -e option is used, client first waits for user input, and then sends CLIENT_HELLO along with the early-data.
The software is provided under the MIT license. Note that additional licences apply if you use the minicrypto binding (see above).
Please report vulnerabilities to h2o-vuln@googlegroups.com. See SECURITY.md for more information.