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- package ct
- import (
- "crypto"
- "crypto/ecdsa"
- "crypto/elliptic"
- "crypto/rsa"
- "crypto/sha256"
- "crypto/x509"
- "encoding/asn1"
- "encoding/pem"
- "errors"
- "flag"
- "fmt"
- "log"
- "math/big"
- )
- var allowVerificationWithNonCompliantKeys = flag.Bool("allow_verification_with_non_compliant_keys", false,
- "Allow a SignatureVerifier to use keys which are technically non-compliant with RFC6962.")
- // PublicKeyFromPEM parses a PEM formatted block and returns the public key contained within and any remaining unread bytes, or an error.
- func PublicKeyFromPEM(b []byte) (crypto.PublicKey, SHA256Hash, []byte, error) {
- p, rest := pem.Decode(b)
- if p == nil {
- return nil, [sha256.Size]byte{}, rest, fmt.Errorf("no PEM block found in %s", string(b))
- }
- k, err := x509.ParsePKIXPublicKey(p.Bytes)
- return k, sha256.Sum256(p.Bytes), rest, err
- }
- // SignatureVerifier can verify signatures on SCTs and STHs
- type SignatureVerifier struct {
- pubKey crypto.PublicKey
- }
- // NewSignatureVerifier creates a new SignatureVerifier using the passed in PublicKey.
- func NewSignatureVerifier(pk crypto.PublicKey) (*SignatureVerifier, error) {
- switch pkType := pk.(type) {
- case *rsa.PublicKey:
- if pkType.N.BitLen() < 2048 {
- e := fmt.Errorf("public key is RSA with < 2048 bits (size:%d)", pkType.N.BitLen())
- if !(*allowVerificationWithNonCompliantKeys) {
- return nil, e
- }
- log.Printf("WARNING: %v", e)
- }
- case *ecdsa.PublicKey:
- params := *(pkType.Params())
- if params != *elliptic.P256().Params() {
- e := fmt.Errorf("public is ECDSA, but not on the P256 curve")
- if !(*allowVerificationWithNonCompliantKeys) {
- return nil, e
- }
- log.Printf("WARNING: %v", e)
- }
- default:
- return nil, fmt.Errorf("Unsupported public key type %v", pkType)
- }
- return &SignatureVerifier{
- pubKey: pk,
- }, nil
- }
- // verifySignature verifies that the passed in signature over data was created by our PublicKey.
- // Currently, only SHA256 is supported as a HashAlgorithm, and only ECDSA and RSA signatures are supported.
- func (s SignatureVerifier) verifySignature(data []byte, sig DigitallySigned) error {
- if sig.HashAlgorithm != SHA256 {
- return fmt.Errorf("unsupported HashAlgorithm in signature: %v", sig.HashAlgorithm)
- }
- hasherType := crypto.SHA256
- hasher := hasherType.New()
- if _, err := hasher.Write(data); err != nil {
- return fmt.Errorf("failed to write to hasher: %v", err)
- }
- hash := hasher.Sum([]byte{})
- switch sig.SignatureAlgorithm {
- case RSA:
- rsaKey, ok := s.pubKey.(*rsa.PublicKey)
- if !ok {
- return fmt.Errorf("cannot verify RSA signature with %T key", s.pubKey)
- }
- if err := rsa.VerifyPKCS1v15(rsaKey, hasherType, hash, sig.Signature); err != nil {
- return fmt.Errorf("failed to verify rsa signature: %v", err)
- }
- case ECDSA:
- ecdsaKey, ok := s.pubKey.(*ecdsa.PublicKey)
- if !ok {
- return fmt.Errorf("cannot verify ECDSA signature with %T key", s.pubKey)
- }
- var ecdsaSig struct {
- R, S *big.Int
- }
- rest, err := asn1.Unmarshal(sig.Signature, &ecdsaSig)
- if err != nil {
- return fmt.Errorf("failed to unmarshal ECDSA signature: %v", err)
- }
- if len(rest) != 0 {
- log.Printf("Garbage following signature %v", rest)
- }
- if !ecdsa.Verify(ecdsaKey, hash, ecdsaSig.R, ecdsaSig.S) {
- return errors.New("failed to verify ecdsa signature")
- }
- default:
- return fmt.Errorf("unsupported signature type %v", sig.SignatureAlgorithm)
- }
- return nil
- }
- // VerifySCTSignature verifies that the SCT's signature is valid for the given LogEntry
- func (s SignatureVerifier) VerifySCTSignature(sct SignedCertificateTimestamp, entry LogEntry) error {
- sctData, err := SerializeSCTSignatureInput(sct, entry)
- if err != nil {
- return err
- }
- return s.verifySignature(sctData, sct.Signature)
- }
- // VerifySTHSignature verifies that the STH's signature is valid.
- func (s SignatureVerifier) VerifySTHSignature(sth SignedTreeHead) error {
- sthData, err := SerializeSTHSignatureInput(sth)
- if err != nil {
- return err
- }
- return s.verifySignature(sthData, sth.TreeHeadSignature)
- }
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