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|
package jwt
import (
"crypto"
"crypto/ecdsa"
"crypto/rand"
"errors"
"math/big"
)
var (
// Sadly this is missing from crypto/ecdsa compared to crypto/rsa
ErrECDSAVerification = errors.New("crypto/ecdsa: verification error")
)
// SigningMethodECDSA implements the ECDSA family of signing methods.
// Expects *ecdsa.PrivateKey for signing and *ecdsa.PublicKey for verification
type SigningMethodECDSA struct {
Name string
Hash crypto.Hash
KeySize int
CurveBits int
}
// Specific instances for EC256 and company
var (
SigningMethodES256 *SigningMethodECDSA
SigningMethodES384 *SigningMethodECDSA
SigningMethodES512 *SigningMethodECDSA
)
func init() {
// ES256
SigningMethodES256 = &SigningMethodECDSA{"ES256", crypto.SHA256, 32, 256}
RegisterSigningMethod(SigningMethodES256.Alg(), func() SigningMethod {
return SigningMethodES256
})
// ES384
SigningMethodES384 = &SigningMethodECDSA{"ES384", crypto.SHA384, 48, 384}
RegisterSigningMethod(SigningMethodES384.Alg(), func() SigningMethod {
return SigningMethodES384
})
// ES512
SigningMethodES512 = &SigningMethodECDSA{"ES512", crypto.SHA512, 66, 521}
RegisterSigningMethod(SigningMethodES512.Alg(), func() SigningMethod {
return SigningMethodES512
})
}
func (m *SigningMethodECDSA) Alg() string {
return m.Name
}
// Verify implements token verification for the SigningMethod.
// For this verify method, key must be an ecdsa.PublicKey struct
func (m *SigningMethodECDSA) Verify(signingString string, sig []byte, key interface{}) error {
// Get the key
var ecdsaKey *ecdsa.PublicKey
switch k := key.(type) {
case *ecdsa.PublicKey:
ecdsaKey = k
default:
return newError("ECDSA verify expects *ecdsa.PublicKey", ErrInvalidKeyType)
}
if len(sig) != 2*m.KeySize {
return ErrECDSAVerification
}
r := big.NewInt(0).SetBytes(sig[:m.KeySize])
s := big.NewInt(0).SetBytes(sig[m.KeySize:])
// Create hasher
if !m.Hash.Available() {
return ErrHashUnavailable
}
hasher := m.Hash.New()
hasher.Write([]byte(signingString))
// Verify the signature
if verifystatus := ecdsa.Verify(ecdsaKey, hasher.Sum(nil), r, s); verifystatus {
return nil
}
return ErrECDSAVerification
}
// Sign implements token signing for the SigningMethod.
// For this signing method, key must be an ecdsa.PrivateKey struct
func (m *SigningMethodECDSA) Sign(signingString string, key interface{}) ([]byte, error) {
// Get the key
var ecdsaKey *ecdsa.PrivateKey
switch k := key.(type) {
case *ecdsa.PrivateKey:
ecdsaKey = k
default:
return nil, newError("ECDSA sign expects *ecdsa.PrivateKey", ErrInvalidKeyType)
}
// Create the hasher
if !m.Hash.Available() {
return nil, ErrHashUnavailable
}
hasher := m.Hash.New()
hasher.Write([]byte(signingString))
// Sign the string and return r, s
if r, s, err := ecdsa.Sign(rand.Reader, ecdsaKey, hasher.Sum(nil)); err == nil {
curveBits := ecdsaKey.Curve.Params().BitSize
if m.CurveBits != curveBits {
return nil, ErrInvalidKey
}
keyBytes := curveBits / 8
if curveBits%8 > 0 {
keyBytes += 1
}
// We serialize the outputs (r and s) into big-endian byte arrays
// padded with zeros on the left to make sure the sizes work out.
// Output must be 2*keyBytes long.
out := make([]byte, 2*keyBytes)
r.FillBytes(out[0:keyBytes]) // r is assigned to the first half of output.
s.FillBytes(out[keyBytes:]) // s is assigned to the second half of output.
return out, nil
} else {
return nil, err
}
}
|
