github.com/aarzilli/tools@v0.0.0-20151123112009-0d27094f75e0/appengine/login/googlesignin/jwt-go/hmac.go (about)

     1  package jwt
     2  
     3  import (
     4  	"crypto"
     5  	"crypto/hmac"
     6  	"errors"
     7  )
     8  
     9  // Implements the HMAC-SHA family of signing methods signing methods
    10  type SigningMethodHMAC struct {
    11  	Name string
    12  	Hash crypto.Hash
    13  }
    14  
    15  // Specific instances for HS256 and company
    16  var (
    17  	SigningMethodHS256  *SigningMethodHMAC
    18  	SigningMethodHS384  *SigningMethodHMAC
    19  	SigningMethodHS512  *SigningMethodHMAC
    20  	ErrSignatureInvalid = errors.New("signature is invalid")
    21  )
    22  
    23  func init() {
    24  	// HS256
    25  	SigningMethodHS256 = &SigningMethodHMAC{"HS256", crypto.SHA256}
    26  	RegisterSigningMethod(SigningMethodHS256.Alg(), func() SigningMethod {
    27  		return SigningMethodHS256
    28  	})
    29  
    30  	// HS384
    31  	SigningMethodHS384 = &SigningMethodHMAC{"HS384", crypto.SHA384}
    32  	RegisterSigningMethod(SigningMethodHS384.Alg(), func() SigningMethod {
    33  		return SigningMethodHS384
    34  	})
    35  
    36  	// HS512
    37  	SigningMethodHS512 = &SigningMethodHMAC{"HS512", crypto.SHA512}
    38  	RegisterSigningMethod(SigningMethodHS512.Alg(), func() SigningMethod {
    39  		return SigningMethodHS512
    40  	})
    41  }
    42  
    43  func (m *SigningMethodHMAC) Alg() string {
    44  	return m.Name
    45  }
    46  
    47  func (m *SigningMethodHMAC) Verify(signingString, signature string, key interface{}) error {
    48  	if keyBytes, ok := key.([]byte); ok {
    49  		var sig []byte
    50  		var err error
    51  		if sig, err = DecodeSegment(signature); err == nil {
    52  			if !m.Hash.Available() {
    53  				return ErrHashUnavailable
    54  			}
    55  
    56  			hasher := hmac.New(m.Hash.New, keyBytes)
    57  			hasher.Write([]byte(signingString))
    58  
    59  			if !hmac.Equal(sig, hasher.Sum(nil)) {
    60  				err = ErrSignatureInvalid
    61  			}
    62  		}
    63  		return err
    64  	}
    65  
    66  	return ErrInvalidKey
    67  }
    68  
    69  // Implements the Sign method from SigningMethod for this signing method.
    70  // Key must be []byte
    71  func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) (string, error) {
    72  	if keyBytes, ok := key.([]byte); ok {
    73  		if !m.Hash.Available() {
    74  			return "", ErrHashUnavailable
    75  		}
    76  
    77  		hasher := hmac.New(m.Hash.New, keyBytes)
    78  		hasher.Write([]byte(signingString))
    79  
    80  		return EncodeSegment(hasher.Sum(nil)), nil
    81  	}
    82  
    83  	return "", ErrInvalidKey
    84  }