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|
package jwt
import (
"crypto"
"crypto/hmac"
"errors"
)
// SigningMethodHMAC implements the HMAC-SHA family of signing methods.
// Expects key type of []byte for both signing and validation
type SigningMethodHMAC struct {
Name string
Hash crypto.Hash
}
// Specific instances for HS256 and company
var (
SigningMethodHS256 *SigningMethodHMAC
SigningMethodHS384 *SigningMethodHMAC
SigningMethodHS512 *SigningMethodHMAC
ErrSignatureInvalid = errors.New("signature is invalid")
)
func init() {
// HS256
SigningMethodHS256 = &SigningMethodHMAC{"HS256", crypto.SHA256}
RegisterSigningMethod(SigningMethodHS256.Alg(), func() SigningMethod {
return SigningMethodHS256
})
// HS384
SigningMethodHS384 = &SigningMethodHMAC{"HS384", crypto.SHA384}
RegisterSigningMethod(SigningMethodHS384.Alg(), func() SigningMethod {
return SigningMethodHS384
})
// HS512
SigningMethodHS512 = &SigningMethodHMAC{"HS512", crypto.SHA512}
RegisterSigningMethod(SigningMethodHS512.Alg(), func() SigningMethod {
return SigningMethodHS512
})
}
func (m *SigningMethodHMAC) Alg() string {
return m.Name
}
// Verify implements token verification for the SigningMethod. Returns nil if
// the signature is valid. Key must be []byte.
//
// Note it is not advised to provide a []byte which was converted from a 'human
// readable' string using a subset of ASCII characters. To maximize entropy, you
// should ideally be providing a []byte key which was produced from a
// cryptographically random source, e.g. crypto/rand. Additional information
// about this, and why we intentionally are not supporting string as a key can
// be found on our usage guide
// https://golang-jwt.github.io/jwt/usage/signing_methods/#signing-methods-and-key-types.
func (m *SigningMethodHMAC) Verify(signingString string, sig []byte, key interface{}) error {
// Verify the key is the right type
keyBytes, ok := key.([]byte)
if !ok {
return newError("HMAC verify expects []byte", ErrInvalidKeyType)
}
// Can we use the specified hashing method?
if !m.Hash.Available() {
return ErrHashUnavailable
}
// This signing method is symmetric, so we validate the signature
// by reproducing the signature from the signing string and key, then
// comparing that against the provided signature.
hasher := hmac.New(m.Hash.New, keyBytes)
hasher.Write([]byte(signingString))
if !hmac.Equal(sig, hasher.Sum(nil)) {
return ErrSignatureInvalid
}
// No validation errors. Signature is good.
return nil
}
// Sign implements token signing for the SigningMethod. Key must be []byte.
//
// Note it is not advised to provide a []byte which was converted from a 'human
// readable' string using a subset of ASCII characters. To maximize entropy, you
// should ideally be providing a []byte key which was produced from a
// cryptographically random source, e.g. crypto/rand. Additional information
// about this, and why we intentionally are not supporting string as a key can
// be found on our usage guide https://golang-jwt.github.io/jwt/usage/signing_methods/.
func (m *SigningMethodHMAC) Sign(signingString string, key interface{}) ([]byte, error) {
if keyBytes, ok := key.([]byte); ok {
if !m.Hash.Available() {
return nil, newError("HMAC sign expects []byte", ErrInvalidKeyType)
}
hasher := hmac.New(m.Hash.New, keyBytes)
hasher.Write([]byte(signingString))
return hasher.Sum(nil), nil
}
return nil, ErrInvalidKeyType
}
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