signature.go

Documentation: github.com/google/certificate-transparency-go/tls

     1  // Copyright 2016 Google LLC. All Rights Reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package tls
    16  
    17  import (
    18  	"crypto"
    19  	"crypto/dsa" //nolint:staticcheck
    20  	"crypto/ecdsa"
    21  	_ "crypto/md5" // For registration side-effect
    22  	"crypto/rand"
    23  	"crypto/rsa"
    24  	_ "crypto/sha1"   // For registration side-effect
    25  	_ "crypto/sha256" // For registration side-effect
    26  	_ "crypto/sha512" // For registration side-effect
    27  	"errors"
    28  	"fmt"
    29  	"log"
    30  	"math/big"
    31  
    32  	"github.com/google/certificate-transparency-go/asn1"
    33  )
    34  
    35  type dsaSig struct {
    36  	R, S *big.Int
    37  }
    38  
    39  func generateHash(algo HashAlgorithm, data []byte) ([]byte, crypto.Hash, error) {
    40  	var hashType crypto.Hash
    41  	switch algo {
    42  	case MD5:
    43  		hashType = crypto.MD5
    44  	case SHA1:
    45  		hashType = crypto.SHA1
    46  	case SHA224:
    47  		hashType = crypto.SHA224
    48  	case SHA256:
    49  		hashType = crypto.SHA256
    50  	case SHA384:
    51  		hashType = crypto.SHA384
    52  	case SHA512:
    53  		hashType = crypto.SHA512
    54  	default:
    55  		return nil, hashType, fmt.Errorf("unsupported Algorithm.Hash in signature: %v", algo)
    56  	}
    57  
    58  	hasher := hashType.New()
    59  	if _, err := hasher.Write(data); err != nil {
    60  		return nil, hashType, fmt.Errorf("failed to write to hasher: %v", err)
    61  	}
    62  	return hasher.Sum([]byte{}), hashType, nil
    63  }
    64  
    65  // VerifySignature verifies that the passed in signature over data was created by the given PublicKey.
    66  func VerifySignature(pubKey crypto.PublicKey, data []byte, sig DigitallySigned) error {
    67  	hash, hashType, err := generateHash(sig.Algorithm.Hash, data)
    68  	if err != nil {
    69  		return err
    70  	}
    71  
    72  	switch sig.Algorithm.Signature {
    73  	case RSA:
    74  		rsaKey, ok := pubKey.(*rsa.PublicKey)
    75  		if !ok {
    76  			return fmt.Errorf("cannot verify RSA signature with %T key", pubKey)
    77  		}
    78  		if err := rsa.VerifyPKCS1v15(rsaKey, hashType, hash, sig.Signature); err != nil {
    79  			return fmt.Errorf("failed to verify rsa signature: %v", err)
    80  		}
    81  	case DSA:
    82  		dsaKey, ok := pubKey.(*dsa.PublicKey)
    83  		if !ok {
    84  			return fmt.Errorf("cannot verify DSA signature with %T key", pubKey)
    85  		}
    86  		var dsaSig dsaSig
    87  		rest, err := asn1.Unmarshal(sig.Signature, &dsaSig)
    88  		if err != nil {
    89  			return fmt.Errorf("failed to unmarshal DSA signature: %v", err)
    90  		}
    91  		if len(rest) != 0 {
    92  			log.Printf("Garbage following signature %q", rest)
    93  		}
    94  		if dsaSig.R.Sign() <= 0 || dsaSig.S.Sign() <= 0 {
    95  			return errors.New("DSA signature contained zero or negative values")
    96  		}
    97  		if !dsa.Verify(dsaKey, hash, dsaSig.R, dsaSig.S) {
    98  			return errors.New("failed to verify DSA signature")
    99  		}
   100  	case ECDSA:
   101  		ecdsaKey, ok := pubKey.(*ecdsa.PublicKey)
   102  		if !ok {
   103  			return fmt.Errorf("cannot verify ECDSA signature with %T key", pubKey)
   104  		}
   105  		var ecdsaSig dsaSig
   106  		rest, err := asn1.Unmarshal(sig.Signature, &ecdsaSig)
   107  		if err != nil {
   108  			return fmt.Errorf("failed to unmarshal ECDSA signature: %v", err)
   109  		}
   110  		if len(rest) != 0 {
   111  			log.Printf("Garbage following signature %q", rest)
   112  		}
   113  		if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
   114  			return errors.New("ECDSA signature contained zero or negative values")
   115  		}
   116  
   117  		if !ecdsa.Verify(ecdsaKey, hash, ecdsaSig.R, ecdsaSig.S) {
   118  			return errors.New("failed to verify ECDSA signature")
   119  		}
   120  	default:
   121  		return fmt.Errorf("unsupported Algorithm.Signature in signature: %v", sig.Algorithm.Hash)
   122  	}
   123  	return nil
   124  }
   125  
   126  // CreateSignature builds a signature over the given data using the specified hash algorithm and private key.
   127  func CreateSignature(privKey crypto.PrivateKey, hashAlgo HashAlgorithm, data []byte) (DigitallySigned, error) {
   128  	var sig DigitallySigned
   129  	sig.Algorithm.Hash = hashAlgo
   130  	hash, hashType, err := generateHash(sig.Algorithm.Hash, data)
   131  	if err != nil {
   132  		return sig, err
   133  	}
   134  
   135  	switch privKey := privKey.(type) {
   136  	case rsa.PrivateKey:
   137  		sig.Algorithm.Signature = RSA
   138  		sig.Signature, err = rsa.SignPKCS1v15(rand.Reader, &privKey, hashType, hash)
   139  		return sig, err
   140  	case ecdsa.PrivateKey:
   141  		sig.Algorithm.Signature = ECDSA
   142  		var ecdsaSig dsaSig
   143  		ecdsaSig.R, ecdsaSig.S, err = ecdsa.Sign(rand.Reader, &privKey, hash)
   144  		if err != nil {
   145  			return sig, err
   146  		}
   147  		sig.Signature, err = asn1.Marshal(ecdsaSig)
   148  		return sig, err
   149  	default:
   150  		return sig, fmt.Errorf("unsupported private key type %T", privKey)
   151  	}
   152  }
   153
View as plain text