The TLS configuration was using Go stdlib defaults — secure for typical
commercial use, but federal evaluators need an explicit cipher
allowlist they can map to a FIPS-validated implementation. Pin the
cipher and curve lists to NIST SP 800-52 Rev. 2 § 3.3 conformant
values:
Ciphers (TLS 1.2):
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305
TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305
Curves: X25519, P-256, P-384
MinVersion: TLS 1.2 (already set; 1.3 used when negotiated)
TLS 1.3 cipher selection is not operator-controllable in Go stdlib
(the runtime picks from a fixed AEAD-only set); all of those
already meet the federal bar so no change needed there.
Also adds HSTSMiddleware emitting `Strict-Transport-Security:
max-age=31536000; includeSubDomains` when zddc-server is itself
terminating TLS (ZDDC_TLS_CERT != none). Behind an upstream proxy
terminating TLS the proxy is responsible for HSTS, so the middleware
only wraps the chain when useTLS=true.
Test coverage:
* TLSConfig(none) returns nil + useTLS=false
* TLSConfig(selfsigned) sets the exact NIST allowlist
* Negative test asserting weak ciphers (CBC, RC4, 3DES, RSA-key-
exchange) are NOT in the list — guardrail against regressions
Federal-readiness gap analysis updated: this control is now partially
complete. OCSP stapling and CT-log inclusion remain on the list for
full DoD STIG conformance.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
ZDDC
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