ssl — TLS over socket

import ssl

TLS 1.2 client + server, backed by axtls. Wraps a regular socket.socket to add encryption and certificate verification.

Quick client

import socket, ssl

s = socket.socket()
s.connect(socket.getaddrinfo('example.com', 443)[0][-1])
ss = ssl.wrap_socket(s, server_hostname='example.com')
ss.write(b'GET / HTTP/1.0\r\nHost: example.com\r\n\r\n')
print(ss.read(4096).decode())
ss.close()

ssl.wrap_socket(sock, *, ...) returns a wrapped socket that quacks like a regular one (.read(), .write(), .close()) but encrypts the wire.

Certificate verification

By default, the wrapper does NO certificate verification — it trusts whatever the server presents. To verify against a CA bundle:

ss = ssl.wrap_socket(
    s,
    server_hostname='example.com',
    cert_reqs=ssl.CERT_REQUIRED,
    ca_certs='CACERTS.PEM',           # path to PEM file
)

If you don’t have a CACERTS.PEM handy, Mozilla’s bundle (the one all your other tools use) is at https://curl.se/ca/cacert.pem. Save it as CACERTS.PEM next to MP.EXE.

ssl.CERT_NONE (default) — don’t verify. ssl.CERT_REQUIRED — verify; raise OSError on failure.

⚠️ On a small DOS system, full chain verification of a real Internet cert chain uses a few hundred KB of axtls heap. If you’re tight on memory, consider trusting a specific server cert directly instead of a full CA bundle.

Server (less common)

srv = socket.socket()
srv.bind(('0.0.0.0', 443))
srv.listen(5)

while True:
    conn, addr = srv.accept()
    ss = ssl.wrap_socket(conn, server_side=True,
                         key='SERVER.KEY', cert='SERVER.PEM')
    ss.write(b'HTTP/1.0 200 OK\r\n\r\nHello!\n')
    ss.close()

SSLContext

ctx = ssl.SSLContext()
ctx.load_verify_locations(cafile='CACERTS.PEM')
ctx.verify_mode = ssl.CERT_REQUIRED

ss = ctx.wrap_socket(sock, server_hostname='example.com')

Same effect as the kwargs version, but reusable across many connections.

Cipher suites

axtls negotiates:

• Key exchange: RSA (P12-style key files), ECDHE on Curve25519
• Bulk: AES-128/256-CBC, AES-128/256-GCM, ChaCha20-Poly1305 NOT supported (chachapoly is stubbed in our axtls adapter)
• MAC: HMAC-SHA256, HMAC-SHA1

The negotiated suite is logged with ssl.SSLContext.set_verify_mode debug builds; users normally don’t need to look.

See also

• socket — the underlying transport
• _ssh — SSH client (separate cryptography stack: axtls + TweetNaCl + libssh2)

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Credit: shape from MicroPython ssl docs (MIT). axtls notes are this port’s.