Kyle Isom
115f23a3ea
Vendor dependencies and expose control program binaries via nix build. Uses nixpkgs-unstable for Go 1.26 support. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
100 lines
3.3 KiB
Go
100 lines
3.3 KiB
Go
package protocol
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import (
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"bytes"
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"crypto/sha256"
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"crypto/x509"
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"encoding/asn1"
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"time"
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"github.com/go-webauthn/webauthn/metadata"
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)
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// attestationFormatValidationHandlerAppleAnonymous is the handler for the Apple Anonymous Attestation Statement Format.
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//
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// The syntax of an Apple attestation statement is defined as follows:
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//
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// $$attStmtType //= (
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//
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// fmt: "apple",
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// attStmt: appleStmtFormat
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// )
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//
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// appleStmtFormat = {
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// x5c: [ credCert: bytes, * (caCert: bytes) ]
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// }
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//
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// Specification: §8.8. Apple Anonymous Attestation Statement Format
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//
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// See : https://www.w3.org/TR/webauthn/#sctn-apple-anonymous-attestation
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func attestationFormatValidationHandlerAppleAnonymous(att AttestationObject, clientDataHash []byte, _ metadata.Provider) (attestationType string, x5cs []any, err error) {
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// Step 1. Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding on it
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// to extract the contained fields.
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var (
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x5c []any
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certs []*x509.Certificate
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)
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if x5c, certs, err = attStatementParseX5CS(att.AttStatement, stmtX5C); err != nil {
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return "", nil, err
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}
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credCert := certs[0]
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if _, err = attStatementCertChainVerify(certs, attAppleHardwareRootsCertPool, true, time.Now().Add(time.Hour*8760).UTC()); err != nil {
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return "", nil, ErrInvalidAttestation.WithDetails("Error validating x5c cert chain").WithError(err)
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}
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// Step 2. Concatenate authenticatorData and clientDataHash to form nonceToHash.
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nonceToHash := append(att.RawAuthData, clientDataHash...) //nolint:gocritic // This is intentional.
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// Step 3. Perform SHA-256 hash of nonceToHash to produce nonce.
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nonce := sha256.Sum256(nonceToHash)
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// Step 4. Verify that nonce equals the value of the extension with OID 1.2.840.113635.100.8.2 in credCert.
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var attExtBytes []byte
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for _, ext := range credCert.Extensions {
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if ext.Id.Equal(oidExtensionAppleAnonymousAttestation) {
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attExtBytes = ext.Value
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}
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}
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if len(attExtBytes) == 0 {
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return "", nil, ErrAttestationFormat.WithDetails("Attestation certificate extensions missing 1.2.840.113635.100.8.2")
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}
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decoded := AppleAnonymousAttestation{}
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if _, err = asn1.Unmarshal(attExtBytes, &decoded); err != nil {
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return "", nil, ErrAttestationFormat.WithDetails("Unable to parse apple attestation certificate extensions").WithError(err)
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}
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if !bytes.Equal(decoded.Nonce, nonce[:]) {
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return "", nil, ErrInvalidAttestation.WithDetails("Attestation certificate does not contain expected nonce")
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}
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// Step 5. Verify that the credential public key equals the Subject Public Key of credCert.
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if _, err = verifyAttestationECDSAPublicKeyMatch(att, credCert); err != nil {
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return "", nil, err
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}
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// Step 6. If successful, return implementation-specific values representing attestation type Anonymization CA and
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// attestation trust path x5c.
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return string(metadata.AnonCA), x5c, nil
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}
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// AppleAnonymousAttestation represents the attestation format for Apple, who have not yet published a schema for the
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// extension (as of JULY 2021.)
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type AppleAnonymousAttestation struct {
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Nonce []byte `asn1:"tag:1,explicit"`
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}
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var (
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attAppleHardwareRootsCertPool *x509.CertPool
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)
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func init() {
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RegisterAttestationFormat(AttestationFormatApple, attestationFormatValidationHandlerAppleAnonymous)
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}
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