Cross-platform RSA & EC keypair generation, signing and verification - suitable for JWT, JOSE, and asymmetric cryptography.
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package keypairs
import (
"crypto"
"crypto/ecdsa"
"crypto/rsa"
"crypto/sha256"
"crypto/subtle"
"encoding/base64"
"errors"
"fmt"
"log"
"math/big"
"time"
)
// VerifyClaims will check the signature of a parsed JWT
func VerifyClaims(pubkey PublicKey, jws *JWS) (errs []error) {
kid, _ := jws.Header["kid"].(string)
jwkmap, hasJWK := jws.Header["jwk"].(Object)
//var jwk JWK = nil
seed, _ := jws.Header["_seed"].(int64)
seedf64, _ := jws.Header["_seed"].(float64)
kty, _ := jws.Header["_kty"].(string)
if 0 == seed {
seed = int64(seedf64)
}
var pub PublicKey = nil
if hasJWK {
pub, errs = selfsignCheck(jwkmap, errs)
} else {
opts := &keyOptions{mockSeed: seed, KeyType: kty}
pub, errs = pubkeyCheck(pubkey, kid, opts, errs)
}
jti, _ := jws.Claims["jti"].(string)
expf64, _ := jws.Claims["exp"].(float64)
exp := int64(expf64)
if 0 == exp {
if "" == jti {
err := errors.New("one of 'jti' or 'exp' must exist for token expiry")
errs = append(errs, err)
}
} else {
if time.Now().Unix() > exp {
err := fmt.Errorf("token expired at %d (%s)", exp, time.Unix(exp, 0))
errs = append(errs, err)
}
}
signable := fmt.Sprintf("%s.%s", jws.Protected, jws.Payload)
hash := sha256.Sum256([]byte(signable))
sig, err := base64.RawURLEncoding.DecodeString(jws.Signature)
if nil != err {
err := fmt.Errorf("could not decode signature: %w", err)
errs = append(errs, err)
return errs
}
//log.Printf("\n(Verify)\nSignable: %s", signable)
//log.Printf("Hash: %s", hash)
//log.Printf("Sig: %s", jws.Signature)
if nil == pub {
err := fmt.Errorf("token signature could not be verified")
errs = append(errs, err)
} else if !Verify(pub, hash[:], sig) {
err := fmt.Errorf("token signature is not valid")
errs = append(errs, err)
}
return errs
}
func selfsignCheck(jwkmap Object, errs []error) (PublicKey, []error) {
var pub PublicKeyDeprecated = nil
log.Println("Security TODO: did not check jws.Claims[\"sub\"] against 'jwk'")
log.Println("Security TODO: did not check jws.Claims[\"iss\"]")
kty := jwkmap["kty"]
var err error
if "RSA" == kty {
e, _ := jwkmap["e"].(string)
n, _ := jwkmap["n"].(string)
k, _ := (&RSAJWK{
Exp: e,
N: n,
}).marshalJWK()
pub, err = ParseJWKPublicKey(k)
if nil != err {
return nil, append(errs, err)
}
} else {
crv, _ := jwkmap["crv"].(string)
x, _ := jwkmap["x"].(string)
y, _ := jwkmap["y"].(string)
k, _ := (&ECJWK{
Curve: crv,
X: x,
Y: y,
}).marshalJWK()
pub, err = ParseJWKPublicKey(k)
if nil != err {
return nil, append(errs, err)
}
}
return pub.Key(), errs
}
func pubkeyCheck(pubkey PublicKey, kid string, opts *keyOptions, errs []error) (PublicKey, []error) {
var pub PublicKey = nil
if "" == kid {
err := errors.New("token should have 'kid' or 'jwk' in header to identify the public key")
errs = append(errs, err)
}
if nil == pubkey {
if allowMocking {
if 0 == opts.mockSeed {
err := errors.New("the debug API requires '_seed' to accompany 'kid'")
errs = append(errs, err)
}
if "" == opts.KeyType {
err := errors.New("the debug API requires '_kty' to accompany '_seed'")
errs = append(errs, err)
}
if 0 == opts.mockSeed || "" == opts.KeyType {
return nil, errs
}
privkey := newPrivateKey(opts)
pub = privkey.Public().(PublicKey)
return pub, errs
}
err := errors.New("no matching public key")
errs = append(errs, err)
} else {
pub = pubkey
}
if nil != pub && "" != kid {
if 1 != subtle.ConstantTimeCompare([]byte(kid), []byte(Thumbprint(pub))) {
err := errors.New("'kid' does not match the public key thumbprint")
errs = append(errs, err)
}
}
return pub, errs
}
// Verify will check the signature of a hash
func Verify(pubkey PublicKey, hash []byte, sig []byte) bool {
switch pub := pubkey.(type) {
case *rsa.PublicKey:
//log.Printf("RSA VERIFY")
// TODO Size(key) to detect key size ?
//alg := "SHA256"
// TODO: this hasn't been tested yet
if err := rsa.VerifyPKCS1v15(pub, crypto.SHA256, hash, sig); nil != err {
return false
}
return true
case *ecdsa.PublicKey:
r := &big.Int{}
r.SetBytes(sig[0:32])
s := &big.Int{}
s.SetBytes(sig[32:])
return ecdsa.Verify(pub, hash, r, s)
default:
panic("impossible condition: non-rsa/non-ecdsa key")
//return false
}
}