/*
Copyright (c) 2009 The Go Authors. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

   * Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
   * Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following disclaimer
in the documentation and/or other materials provided with the
distribution.
   * Neither the name of Google Inc. nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package x509util

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rsa"
	_ "crypto/sha256" // support SHA256
	_ "crypto/sha512" // support SHA512
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/asn1"
	"errors"
	"io"
)

type CertificateRequest struct {
	x509.CertificateRequest

	ChallengePassword string
}

// CreateCertificateRequest creates a new certificate request based on a template.
// The resulting CSR is similar to x509 but optionally supports the
// challengePassword attribute.
//
// See https://github.com/golang/go/issues/15995
func CreateCertificateRequest(rand io.Reader, template *CertificateRequest, priv crypto.PrivateKey) (csr []byte, err error) {
	if template.ChallengePassword == "" {
		// if no challenge password, return a stdlib CSR.
		return x509.CreateCertificateRequest(rand, &template.CertificateRequest, priv)
	}
	derBytes, err := x509.CreateCertificateRequest(rand, &template.CertificateRequest, priv)
	if err != nil {
		return nil, err
	}
	// add the challenge attribute to the CSR, then re-sign the raw csr.
	// not checking the crypto.Signer assertion because x509.CreateCertificateRequest already did that.
	return addChallenge(
		template.CertificateRequest.SignatureAlgorithm,
		rand,
		derBytes,
		template.ChallengePassword,
		priv.(crypto.Signer),
	)
}

type passwordChallengeAttribute struct {
	Type  asn1.ObjectIdentifier
	Value []string `asn1:"set"`
}

// The structures below are copied from the Go standard library x509 package.

type publicKeyInfo struct {
	Raw       asn1.RawContent
	Algorithm pkix.AlgorithmIdentifier
	PublicKey asn1.BitString
}

type tbsCertificateRequest struct {
	Raw           asn1.RawContent
	Version       int
	Subject       asn1.RawValue
	PublicKey     publicKeyInfo
	RawAttributes []asn1.RawValue `asn1:"tag:0"`
}

type certificateRequest struct {
	Raw                asn1.RawContent
	TBSCSR             tbsCertificateRequest
	SignatureAlgorithm pkix.AlgorithmIdentifier
	SignatureValue     asn1.BitString
}

// ParseChallengePassword extracts the challengePassword attribute from a
// DER encoded Certificate Signing Request.
func ParseChallengePassword(asn1Data []byte) (string, error) {
	type attribute struct {
		ID    asn1.ObjectIdentifier
		Value asn1.RawValue `asn1:"set"`
	}
	var csr certificateRequest
	rest, err := asn1.Unmarshal(asn1Data, &csr)
	if err != nil {
		return "", err
	} else if len(rest) != 0 {
		err = asn1.SyntaxError{Msg: "trailing data"}
		return "", err
	}

	var password string
	for _, rawAttr := range csr.TBSCSR.RawAttributes {
		var attr attribute
		_, err := asn1.Unmarshal(rawAttr.FullBytes, &attr)
		if err != nil {
			return "", err
		}
		if attr.ID.Equal(oidChallengePassword) {
			_, err := asn1.Unmarshal(attr.Value.Bytes, &password)
			if err != nil {
				return "", err
			}
		}
	}

	return password, nil
}

// addChallenge takes a raw CSR created by x509.CreateCertificateRequest,
// adds a passwordChallengeAttribute and re-signs the raw CSR bytes.
func addChallenge(
	templateSigAlgo x509.SignatureAlgorithm,
	reader io.Reader,
	derBytes []byte,
	challenge string,
	key crypto.Signer,
) (csr []byte, err error) {
	var hashFunc crypto.Hash
	var sigAlgo pkix.AlgorithmIdentifier
	hashFunc, sigAlgo, err = signingParamsForPublicKey(key.Public(), templateSigAlgo)
	if err != nil {
		return nil, err
	}

	var req certificateRequest
	rest, err := asn1.Unmarshal(derBytes, &req)
	if err != nil {
		return nil, err
	} else if len(rest) != 0 {
		err = asn1.SyntaxError{Msg: "trailing data"}
		return nil, err
	}

	passwordAttribute := passwordChallengeAttribute{
		Type:  oidChallengePassword,
		Value: []string{challenge},
	}
	b, err := asn1.Marshal(passwordAttribute)
	if err != nil {
		return nil, err
	}

	var rawAttribute asn1.RawValue
	rest, err = asn1.Unmarshal(b, &rawAttribute)
	if err != nil {
		return nil, err
	} else if len(rest) != 0 {
		err = asn1.SyntaxError{Msg: "trailing data"}
		return nil, err
	}

	// append attribute
	req.TBSCSR.RawAttributes = append(req.TBSCSR.RawAttributes, rawAttribute)

	// recreate request
	tbsCSR := tbsCertificateRequest{
		Version:       0,
		Subject:       req.TBSCSR.Subject,
		PublicKey:     req.TBSCSR.PublicKey,
		RawAttributes: req.TBSCSR.RawAttributes,
	}

	tbsCSRContents, err := asn1.Marshal(tbsCSR)
	if err != nil {
		return nil, err
	}
	tbsCSR.Raw = tbsCSRContents

	h := hashFunc.New()
	if _, err := h.Write(tbsCSRContents); err != nil {
		return nil, err
	}

	var signature []byte
	signature, err = key.Sign(reader, h.Sum(nil), hashFunc)
	if err != nil {
		return nil, err
	}

	return asn1.Marshal(certificateRequest{
		TBSCSR:             tbsCSR,
		SignatureAlgorithm: sigAlgo,
		SignatureValue: asn1.BitString{
			Bytes:     signature,
			BitLength: len(signature) * 8,
		},
	})
}

// signingParamsForPublicKey returns the parameters to use for signing with
// priv. If requestedSigAlgo is not zero then it overrides the default
// signature algorithm.
func signingParamsForPublicKey(pub interface{}, requestedSigAlgo x509.SignatureAlgorithm) (hashFunc crypto.Hash, sigAlgo pkix.AlgorithmIdentifier, err error) {
	var pubType x509.PublicKeyAlgorithm

	switch pub := pub.(type) {
	case *rsa.PublicKey:
		pubType = x509.RSA
		hashFunc = crypto.SHA256
		sigAlgo.Algorithm = oidSignatureSHA256WithRSA
		sigAlgo.Parameters = asn1NullRawValue

	case *ecdsa.PublicKey:
		pubType = x509.ECDSA

		switch pub.Curve {
		case elliptic.P224(), elliptic.P256():
			hashFunc = crypto.SHA256
			sigAlgo.Algorithm = oidSignatureECDSAWithSHA256
		case elliptic.P384():
			hashFunc = crypto.SHA384
			sigAlgo.Algorithm = oidSignatureECDSAWithSHA384
		case elliptic.P521():
			hashFunc = crypto.SHA512
			sigAlgo.Algorithm = oidSignatureECDSAWithSHA512
		default:
			err = errors.New("x509: unknown elliptic curve")
		}

	default:
		err = errors.New("x509: only RSA and ECDSA keys supported")
	}

	if err != nil {
		return
	}

	if requestedSigAlgo == 0 {
		return
	}

	found := false
	for _, details := range signatureAlgorithmDetails {
		if details.algo != requestedSigAlgo {
			continue
		}

		if details.pubKeyAlgo != pubType {
			err = errors.New("x509: requested SignatureAlgorithm does not match private key type")
			return
		}
		sigAlgo.Algorithm, hashFunc = details.oid, details.hash
		if hashFunc == 0 {
			err = errors.New("x509: cannot sign with hash function requested")
			return
		}
		// copy x509.SignatureAlgorithm.isRSAPSS method
		isRSAPSS := func() bool {
			switch requestedSigAlgo {
			case x509.SHA256WithRSAPSS, x509.SHA384WithRSAPSS, x509.SHA512WithRSAPSS:
				return true
			default:
				return false
			}
		}
		if isRSAPSS() {
			sigAlgo.Parameters = rsaPSSParameters(hashFunc)
		}
		found = true
		break
	}

	if !found {
		err = errors.New("x509: unknown SignatureAlgorithm")
	}

	return
}

var signatureAlgorithmDetails = []struct {
	algo       x509.SignatureAlgorithm
	oid        asn1.ObjectIdentifier
	pubKeyAlgo x509.PublicKeyAlgorithm
	hash       crypto.Hash
}{
	{x509.SHA256WithRSA, oidSignatureSHA256WithRSA, x509.RSA, crypto.SHA256},
	{x509.SHA384WithRSA, oidSignatureSHA384WithRSA, x509.RSA, crypto.SHA384},
	{x509.SHA512WithRSA, oidSignatureSHA512WithRSA, x509.RSA, crypto.SHA512},
	{x509.SHA256WithRSAPSS, oidSignatureRSAPSS, x509.RSA, crypto.SHA256},
	{x509.SHA384WithRSAPSS, oidSignatureRSAPSS, x509.RSA, crypto.SHA384},
	{x509.SHA512WithRSAPSS, oidSignatureRSAPSS, x509.RSA, crypto.SHA512},
	{x509.DSAWithSHA256, oidSignatureDSAWithSHA256, x509.DSA, crypto.SHA256},
	{x509.ECDSAWithSHA256, oidSignatureECDSAWithSHA256, x509.ECDSA, crypto.SHA256},
	{x509.ECDSAWithSHA384, oidSignatureECDSAWithSHA384, x509.ECDSA, crypto.SHA384},
	{x509.ECDSAWithSHA512, oidSignatureECDSAWithSHA512, x509.ECDSA, crypto.SHA512},
}

var (
	oidSignatureSHA256WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 11}
	oidSignatureSHA384WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 12}
	oidSignatureSHA512WithRSA   = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 13}
	oidSignatureRSAPSS          = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 10}
	oidSignatureDSAWithSHA256   = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 3, 2}
	oidSignatureECDSAWithSHA256 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 2}
	oidSignatureECDSAWithSHA384 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 3}
	oidSignatureECDSAWithSHA512 = asn1.ObjectIdentifier{1, 2, 840, 10045, 4, 3, 4}

	oidSHA256 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 1}
	oidSHA384 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 2}
	oidSHA512 = asn1.ObjectIdentifier{2, 16, 840, 1, 101, 3, 4, 2, 3}

	oidMGF1 = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 1, 8}

	oidChallengePassword = asn1.ObjectIdentifier{1, 2, 840, 113549, 1, 9, 7}
)

// added to Go in 1.9
var asn1NullRawValue = asn1.RawValue{
	Tag: 5, /* ASN.1 NULL */
}

// pssParameters reflects the parameters in an AlgorithmIdentifier that
// specifies RSA PSS. See https://tools.ietf.org/html/rfc3447#appendix-A.2.3
type pssParameters struct {
	// The following three fields are not marked as
	// optional because the default values specify SHA-1,
	// which is no longer suitable for use in signatures.
	Hash         pkix.AlgorithmIdentifier `asn1:"explicit,tag:0"`
	MGF          pkix.AlgorithmIdentifier `asn1:"explicit,tag:1"`
	SaltLength   int                      `asn1:"explicit,tag:2"`
	TrailerField int                      `asn1:"optional,explicit,tag:3,default:1"`
}

// rsaPSSParameters returns an asn1.RawValue suitable for use as the Parameters
// in an AlgorithmIdentifier that specifies RSA PSS.
func rsaPSSParameters(hashFunc crypto.Hash) asn1.RawValue {
	var hashOID asn1.ObjectIdentifier

	switch hashFunc {
	case crypto.SHA256:
		hashOID = oidSHA256
	case crypto.SHA384:
		hashOID = oidSHA384
	case crypto.SHA512:
		hashOID = oidSHA512
	}

	params := pssParameters{
		Hash: pkix.AlgorithmIdentifier{
			Algorithm:  hashOID,
			Parameters: asn1NullRawValue,
		},
		MGF: pkix.AlgorithmIdentifier{
			Algorithm: oidMGF1,
		},
		SaltLength:   hashFunc.Size(),
		TrailerField: 1,
	}

	mgf1Params := pkix.AlgorithmIdentifier{
		Algorithm:  hashOID,
		Parameters: asn1NullRawValue,
	}

	var err error
	params.MGF.Parameters.FullBytes, err = asn1.Marshal(mgf1Params)
	if err != nil {
		panic(err)
	}

	serialized, err := asn1.Marshal(params)
	if err != nil {
		panic(err)
	}

	return asn1.RawValue{FullBytes: serialized}
}