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High riskScanned 2026-05-29

GnuTLS — Post-Quantum Cryptography Analysis

gnutls/gnutls ↗|C|1640 files scanned|89 vulnerable

GnuTLS is a widely-deployed TLS library used in Linux distributions, GNOME, and server software. It supports RSA, ECDSA, and DHE — all quantum-vulnerable for key establishment. GnuTLS 3.8.x added experimental support for X25519 MLKEM (hybrid PQC) in TLS 1.3, but this is not default. The majority of deployed GnuTLS configurations use classical algorithms exclusively.

78
/ 100 risk score
High risk
Critical findings1
High findings2
Medium findings1
Low findings0

Findings

criticalRSA-2048 (TLS key exchange / certificates)
lib/pk.c

Default RSA key size. TLS handshakes using RSA key exchange are vulnerable to HNDL attacks.

PQC →ML-KEM-768 hybrid for TLS 1.3 key exchange (X25519MLKEM768).
highECDHE P-256 (default key exchange)
lib/handshake.c

TLS 1.3 default cipher suite uses ECDHE for forward secrecy — quantum-vulnerable.

PQC →Enable `GNUTLS_KX_MLKEM768X25519` cipher suite (available in GnuTLS 3.8.6+).
highDHE (TLS 1.2 compatibility)
lib/dh.c

Finite-field Diffie-Hellman. Quantum-vulnerable, also weak for short groups (<3072 bits).

PQC →Disable DHE; migrate to TLS 1.3 + ML-KEM hybrid.
mediumECDSA certificate validation
lib/x509/verify.c

Certificate chain validation using ECDSA signatures. Quantum-vulnerable for long-lived CAs.

PQC →ML-DSA-44 for TLS certificates when browser/CA support matures.

Compliance note

TLS libraries are a top priority for post-quantum migration — they protect data in transit for billions of connections. HNDL (Harvest Now, Decrypt Later) attacks mean data transmitted today over classical TLS can be decrypted when quantum hardware matures. Enable GnuTLS hybrid PQC mode for all new deployments.

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