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Allow configuration of TLS policy: implementation
Signed-off-by: Hugo Landau <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,145 @@ | ||
| // Package tlspolicy provides for configuration and enforcement of policies | ||
| // relating to TLS. | ||
| package tlspolicy | ||
|
|
||
| import ( | ||
| "crypto/tls" | ||
| "errors" | ||
| "fmt" | ||
|
|
||
| "github.com/hashicorp/go-hclog" | ||
| ) | ||
|
|
||
| // SupportsPQKEM is a constant indicating whether the version of Go used to | ||
| // build, and the build configuration, supports a post-quantum safe TLS key | ||
| // exchange method. | ||
| const SupportsPQKEM = supportsPQKEM | ||
|
|
||
| // Post-quantum TLS KEM mode. Determines whether a post-quantum safe KEM should | ||
| // be used when establishing a TLS connection. | ||
| type PQKEMMode int | ||
|
|
||
| const ( | ||
| // Do not require use of a post-quantum KEM when establishing a TLS | ||
| // connection. Whether a post-quantum KEM is attempted depends on | ||
| // environmental configuration (e.g. GODEBUG setting tlskyber) and the target | ||
| // Go version at build time. | ||
| PQKEMModeDefault PQKEMMode = iota | ||
|
|
||
| // Attempt use of a post-quantum KEM as the most preferred key exchange | ||
| // method when establishing a TLS connection. | ||
| // Support for this requires Go 1.23 or later. | ||
| // Configuring this will cause connections to fail if support is not available. | ||
| PQKEMModeAttempt | ||
|
|
||
| // Require use of a post-quantum KEM when establishing a TLS connection. | ||
| // Attempts to initiate a connection with a key exchange method which is not | ||
| // post-quantum safe will fail. Support for this requires Go 1.23 or later. | ||
| // Configuring this will cause connections to fail if support is not available. | ||
| PQKEMModeRequire | ||
| ) | ||
|
|
||
| // ParsePQKEMMode parses a string into a PQKEMMode value or returns | ||
| // an error. | ||
| func ParsePQKEMMode(logger hclog.Logger, value string) (mode PQKEMMode, err error) { | ||
| if value != "" { | ||
| logger.Warn("pq_kem_mode is experimental and may be changed or removed in a future release") | ||
| } | ||
|
|
||
| switch value { | ||
| case "": | ||
| if SupportsPQKEM { | ||
| logger.Debug("pq_kem_mode supported in this build; post-quantum-safe TLS key exchange may or may not be used depending on system configuration") | ||
| } else { | ||
| logger.Debug("pq_kem_mode not supported in this build") | ||
| } | ||
| return | ||
|
|
||
| case "default": | ||
| if SupportsPQKEM { | ||
| logger.Debug("pq_kem_mode supported and explicitly set to 'default'; post-quantum-safe TLS key exchange may or may not be used depending on system configuration") | ||
| } else { | ||
| logger.Debug("pq_kem_mode explicitly set to 'default'; post-quantum-safe TLS key exchange not supported in this build") | ||
| } | ||
| return | ||
|
|
||
| case "attempt": | ||
| if !SupportsPQKEM { | ||
| logger.Warn("pq_kem_mode set to 'attempt' but no post-quantum-safe key exchange methods are supported in this build (requires Go 1.23); ignoring") | ||
| return | ||
| } | ||
|
|
||
| logger.Debug("pq_kem_mode supported and configured in 'attempt' mode") | ||
| mode = PQKEMModeAttempt | ||
| return | ||
|
|
||
| case "require": | ||
| if !SupportsPQKEM { | ||
| err = errors.New("pq_kem_mode set to 'require' but not supported in this build; requires Go 1.23") | ||
| logger.Error(err.Error()) | ||
| return | ||
| } | ||
|
|
||
| logger.Debug("pq_kem_mode supported and configured in 'require' mode - will require post-quantum security for all TLS connections") | ||
| mode = PQKEMModeRequire | ||
| return | ||
|
|
||
| default: | ||
| mode = PQKEMModeDefault | ||
| err = fmt.Errorf("pq_kem_mode of %q is invalid; must be one of ['', 'default', 'attempt', 'require']", value) | ||
| return | ||
| } | ||
| } | ||
|
|
||
| // Policy describes policy options to be applied to a TLS configuration. | ||
| // | ||
| // A zero-initialised Policy provides reasonable defaults. | ||
| type Policy struct { | ||
| // PQKEMMode specifies the post-quantum KEM policy to use. | ||
| PQKEMMode PQKEMMode | ||
| } | ||
|
|
||
| // Not exported by crypto/tls, so we define it here from the I-D. | ||
| const x25519Kyber768Draft00 tls.CurveID = 0x6399 | ||
|
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| // ApplyPolicy applies the policy options in policy to a given tls.Config, | ||
| // which is assumed to have already been obtained from the go-spiffe | ||
| // tlsconfig package. | ||
| func ApplyPolicy(config *tls.Config, policy Policy) error { | ||
| // Apply post-quantum KEM mode option. | ||
| switch policy.PQKEMMode { | ||
| case PQKEMModeDefault: | ||
| // Nothing to do - allow default curve preferences. | ||
|
|
||
| case PQKEMModeAttempt: | ||
| if len(config.CurvePreferences) == 0 { | ||
| // This is copied from the crypto/tls default curve list. | ||
| config.CurvePreferences = []tls.CurveID{ | ||
| x25519Kyber768Draft00, | ||
| tls.X25519, | ||
| tls.CurveP256, | ||
| tls.CurveP384, | ||
| tls.CurveP521, | ||
| } | ||
| } else if config.CurvePreferences[0] != x25519Kyber768Draft00 { | ||
| // Prepend X25519Kyber768Draft00 to the list, making it most preferred. | ||
| curves := make([]tls.CurveID, 0, len(config.CurvePreferences)+1) | ||
| curves = append(curves, x25519Kyber768Draft00) | ||
| curves = append(curves, config.CurvePreferences...) | ||
| config.CurvePreferences = curves | ||
| } | ||
|
|
||
| case PQKEMModeRequire: | ||
| // List only known PQ-safe KEMs as valid curves. | ||
| config.CurvePreferences = []tls.CurveID{ | ||
| x25519Kyber768Draft00, | ||
| } | ||
|
|
||
| // Require TLS 1.3, as all PQ-safe KEMs require it anyway. | ||
| if config.MinVersion < tls.VersionTLS13 { | ||
| config.MinVersion = tls.VersionTLS13 | ||
| } | ||
| } | ||
|
|
||
| return nil | ||
| } |
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