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