97 lines
2.8 KiB
Go
97 lines
2.8 KiB
Go
package crypto
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import (
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"crypto/ecdsa"
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"crypto/sha256"
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"fmt"
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"math/big"
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"git.frostfs.info/TrueCloudLab/frostfs-crypto/internal"
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"git.frostfs.info/TrueCloudLab/rfc6979"
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)
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const (
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// RFC6979SignatureSize contains r and s coordinates (32 bytes)
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RFC6979SignatureSize = 64
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// ErrWrongHashSize when passed signature to VerifyRFC6979 has wrong size.
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ErrWrongHashSize = internal.Error("wrong hash size")
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// ErrWrongSignature when passed signature to VerifyRFC6979 isn't valid.
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ErrWrongSignature = internal.Error("wrong signature")
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)
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// hashBytesRFC6979 returns the sha256 sum.
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func hashBytesRFC6979(data []byte) []byte {
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sign := sha256.Sum256(data)
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return sign[:]
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}
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// SignRFC6979 signs an arbitrary length hash (which should be the result of
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// hashing a larger message) using the private key. It returns the
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// signature as a pair of integers.
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//
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// Note that FIPS 186-3 section 4.6 specifies that the hash should be truncated
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// to the byte-length of the subgroup. This function does not perform that.
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func SignRFC6979(key *ecdsa.PrivateKey, msg []byte) ([]byte, error) {
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return SignRFC6979Hash(key, hashBytesRFC6979(msg))
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}
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// SignRFC6979Hash signs sha256 hash of the message using the private key.
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func SignRFC6979Hash(key *ecdsa.PrivateKey, msgHash []byte) ([]byte, error) {
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if key == nil {
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return nil, ErrEmptyPrivateKey
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}
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r, s := rfc6979.SignECDSA(key, msgHash, sha256.New)
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rBytes, sBytes := r.Bytes(), s.Bytes()
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signature := make([]byte, RFC6979SignatureSize)
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// if `r` has less than 32 bytes, add leading zeros
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ind := RFC6979SignatureSize/2 - len(rBytes)
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copy(signature[ind:], rBytes)
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// if `s` has less than 32 bytes, add leading zeros
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ind = RFC6979SignatureSize - len(sBytes)
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copy(signature[ind:], sBytes)
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return signature, nil
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}
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func decodeSignature(sig []byte) (*big.Int, *big.Int, error) {
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if ln := len(sig); ln != RFC6979SignatureSize {
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return nil, nil, fmt.Errorf("%w: actual=%d, expect=%d",
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ErrWrongHashSize, ln, RFC6979SignatureSize)
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}
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return new(big.Int).SetBytes(sig[:32]), new(big.Int).SetBytes(sig[32:]), nil
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}
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// VerifyRFC6979 verifies the signature of msg using the public key. It
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// return nil only if signature is valid.
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func VerifyRFC6979(key *ecdsa.PublicKey, msg, sig []byte) error {
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if key == nil {
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return ErrEmptyPublicKey
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} else if r, s, err := decodeSignature(sig); err != nil {
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return err
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} else if !ecdsa.Verify(key, hashBytesRFC6979(msg), r, s) {
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return ErrWrongSignature
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}
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return nil
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}
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// VerifyRFC6979 verifies the signature of msg using the public key. It
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// return nil only if signature is valid.
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func VerifyRFC6979Hash(key *ecdsa.PublicKey, msgHash, sig []byte) error {
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if key == nil {
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return ErrEmptyPublicKey
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} else if r, s, err := decodeSignature(sig); err != nil {
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return err
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} else if !ecdsa.Verify(key, msgHash, r, s) {
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return ErrWrongSignature
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}
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return nil
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}
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