pubkeypin.go

Documentation: k8s.io/kubernetes/cmd/kubeadm/app/util/pubkeypin

     1  /*
     2  Copyright 2017 The Kubernetes Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  // Package pubkeypin provides primitives for x509 public key pinning in the
    18  // style of RFC7469.
    19  package pubkeypin
    20  
    21  import (
    22  	"crypto/sha256"
    23  	"crypto/x509"
    24  	"encoding/hex"
    25  	"strings"
    26  
    27  	"github.com/pkg/errors"
    28  )
    29  
    30  const (
    31  	// formatSHA256 is the prefix for pins that are full-length SHA-256 hashes encoded in base 16 (hex)
    32  	formatSHA256 = "sha256"
    33  )
    34  
    35  var (
    36  	// supportedFormats enumerates the supported formats
    37  	supportedFormats = strings.Join([]string{formatSHA256}, ", ")
    38  )
    39  
    40  // Set is a set of pinned x509 public keys.
    41  type Set struct {
    42  	sha256Hashes map[string]bool
    43  }
    44  
    45  // NewSet returns a new, empty PubKeyPinSet
    46  func NewSet() *Set {
    47  	return &Set{make(map[string]bool)}
    48  }
    49  
    50  // Allow adds an allowed public key hash to the Set
    51  func (s *Set) Allow(pubKeyHashes ...string) error {
    52  	for _, pubKeyHash := range pubKeyHashes {
    53  		parts := strings.Split(pubKeyHash, ":")
    54  		if len(parts) != 2 {
    55  			return errors.Errorf("invalid hash, expected \"format:hex-value\". "+
    56  				"Known format(s) are: %s", supportedFormats)
    57  		}
    58  		format, value := parts[0], parts[1]
    59  
    60  		switch strings.ToLower(format) {
    61  		case "sha256":
    62  			if err := s.allowSHA256(value); err != nil {
    63  				return errors.Errorf("invalid hash %q, %v", pubKeyHash, err)
    64  			}
    65  		default:
    66  			return errors.Errorf("unknown hash format %q. Known format(s) are: %s", format, supportedFormats)
    67  		}
    68  	}
    69  	return nil
    70  }
    71  
    72  // CheckAny checks if at least one certificate matches one of the public keys in the set
    73  func (s *Set) CheckAny(certificates []*x509.Certificate) error {
    74  	var hashes []string
    75  
    76  	for _, certificate := range certificates {
    77  		if s.checkSHA256(certificate) {
    78  			return nil
    79  		}
    80  
    81  		hashes = append(hashes, Hash(certificate))
    82  	}
    83  	return errors.Errorf("none of the public keys %q are pinned", strings.Join(hashes, ":"))
    84  }
    85  
    86  // Empty returns true if the Set contains no pinned public keys.
    87  func (s *Set) Empty() bool {
    88  	return len(s.sha256Hashes) == 0
    89  }
    90  
    91  // Hash calculates the SHA-256 hash of the Subject Public Key Information (SPKI)
    92  // object in an x509 certificate (in DER encoding). It returns the full hash as a
    93  // hex encoded string (suitable for passing to Set.Allow).
    94  func Hash(certificate *x509.Certificate) string {
    95  	spkiHash := sha256.Sum256(certificate.RawSubjectPublicKeyInfo)
    96  	return formatSHA256 + ":" + strings.ToLower(hex.EncodeToString(spkiHash[:]))
    97  }
    98  
    99  // allowSHA256 validates a "sha256" format hash and adds a canonical version of it into the Set
   100  func (s *Set) allowSHA256(hash string) error {
   101  	// validate that the hash is the right length to be a full SHA-256 hash
   102  	hashLength := hex.DecodedLen(len(hash))
   103  	if hashLength != sha256.Size {
   104  		return errors.Errorf("expected a %d byte SHA-256 hash, found %d bytes", sha256.Size, hashLength)
   105  	}
   106  
   107  	// validate that the hash is valid hex
   108  	_, err := hex.DecodeString(hash)
   109  	if err != nil {
   110  		return errors.Wrap(err, "could not decode SHA-256 from hex")
   111  	}
   112  
   113  	// in the end, just store the original hex string in memory (in lowercase)
   114  	s.sha256Hashes[strings.ToLower(hash)] = true
   115  	return nil
   116  }
   117  
   118  // checkSHA256 returns true if the certificate's "sha256" hash is pinned in the Set
   119  func (s *Set) checkSHA256(certificate *x509.Certificate) bool {
   120  	actualHash := sha256.Sum256(certificate.RawSubjectPublicKeyInfo)
   121  	actualHashHex := strings.ToLower(hex.EncodeToString(actualHash[:]))
   122  	return s.sha256Hashes[actualHashHex]
   123  }
   124
View as plain text