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// Copyright 2024 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package rsassapss
import (
"bytes"
"crypto/rsa"
"fmt"
"math/big"
"github.com/tink-crypto/tink-go/v2/insecuresecretdataaccess"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/internal/outputprefix"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/secretdata"
)
// Variant is the prefix variant of an RSA-SSA-PSS key.
//
// It describes the format of the signature. For RSA-SSA-PSS there are
// four options:
//
// - TINK: prepends '0x01<big endian key id>' to the signature.
// - CRUNCHY: prepends '0x00<big endian key id>' to the signature.
// - LEGACY: appends a 0-byte to the input message before computing the
// signature, then prepends '0x00<big endian key id>' to the signature.
// - NO_PREFIX: adds no prefix to the signature.
type Variant int
const (
// VariantUnknown is the default value of Variant.
VariantUnknown Variant = iota
// VariantTink prefixes '0x01<big endian key id>' to the signature.
VariantTink
// VariantCrunchy prefixes '0x00<big endian key id>' to the signature.
VariantCrunchy
// VariantLegacy appends a 0-byte to input message BEFORE computing the signature,
// signature, then prepends '0x00<big endian key id>' to signature.
VariantLegacy
// VariantNoPrefix does not prefix the signature with the key id.
VariantNoPrefix
)
func (variant Variant) String() string {
switch variant {
case VariantTink:
return "TINK"
case VariantCrunchy:
return "CRUNCHY"
case VariantLegacy:
return "LEGACY"
case VariantNoPrefix:
return "NO_PREFIX"
default:
return "UNKNOWN"
}
}
// HashType is the curve type of the RSA-SSA-PSS key.
type HashType int
const (
// UnknownHashType is the default value of HashType.
UnknownHashType HashType = iota
// SHA256 is the SHA256 hash type.
SHA256
// SHA384 is the SHA384 hash type.
SHA384
// SHA512 is the SHA512 hash type.
SHA512
)
func (ht HashType) String() string {
switch ht {
case SHA256:
return "SHA256"
case SHA384:
return "SHA384"
case SHA512:
return "SHA512"
default:
return "UNKNOWN"
}
}
const (
// f4 is the public exponent 65537.
f4 = 65537
maxExponent = 1<<31 - 1
)
// Parameters represents the parameters of an RSA-SSA-PSS key.
type Parameters struct {
modulusSizeBits int
sigHashType HashType
mgf1HashType HashType
publicExponent int
saltLengthBytes int
variant Variant
}
var _ key.Parameters = (*Parameters)(nil)
// SigHashType returns the signature hash type.
func (p *Parameters) SigHashType() HashType { return p.sigHashType }
// MGF1HashType returns the MGF1 hash type.
func (p *Parameters) MGF1HashType() HashType { return p.mgf1HashType }
// PublicExponent returns the public exponent.
func (p *Parameters) PublicExponent() int { return p.publicExponent }
// SaltLengthBytes returns the salt length in bytes.
func (p *Parameters) SaltLengthBytes() int { return p.saltLengthBytes }
// ModulusSizeBits returns the modulus size in bits.
func (p *Parameters) ModulusSizeBits() int { return p.modulusSizeBits }
// Variant returns the output prefix variant of the key.
func (p *Parameters) Variant() Variant { return p.variant }
func checkValidHash(hashType HashType) error {
if hashType == SHA256 || hashType == SHA384 || hashType == SHA512 {
return nil
}
return fmt.Errorf("unsupported hash type: %v", hashType)
}
// ParametersValues contains the values of a set of RSA-SSA-PSS parameters.
type ParametersValues struct {
ModulusSizeBits int
SigHashType HashType
MGF1HashType HashType
PublicExponent int
SaltLengthBytes int
}
// NewParameters creates a new RSA-SSA-PSS Parameters value.
func NewParameters(values ParametersValues, variant Variant) (*Parameters, error) {
// These are consistent with the checks by tink-java and tink-cc.
if values.ModulusSizeBits < 2048 {
return nil, fmt.Errorf("rsassapss.NewParameters: invalid modulus size: %v, want >= 2048", values.ModulusSizeBits)
}
if values.PublicExponent < f4 {
return nil, fmt.Errorf("rsassapss.NewParameters: invalid public exponent: %v, want >= %v", values.PublicExponent, f4)
}
// Similar check as in crypto/rsa.
if values.PublicExponent > maxExponent {
return nil, fmt.Errorf("rsassapss.NewParameters: invalid public exponent: %v, want <= %v", values.PublicExponent, maxExponent)
}
// These are consistent with the checks by tink-java and tink-cc.
if values.PublicExponent%2 != 1 {
return nil, fmt.Errorf("rsassapss.NewParameters: invalid public exponent: %v, want odd", values.PublicExponent)
}
if values.SaltLengthBytes < 0 {
return nil, fmt.Errorf("rsassapss.NewParameters: invalid salt length bytes: %v, want >= 0", values.SaltLengthBytes)
}
if err := checkValidHash(values.SigHashType); err != nil {
return nil, err
}
if values.MGF1HashType != values.SigHashType {
return nil, fmt.Errorf("rsassapss.NewParameters: mismatched MGF1 hash type: %v, want %v", values.MGF1HashType, values.SigHashType)
}
if variant == VariantUnknown {
return nil, fmt.Errorf("unsupported output prefix variant: %v", variant)
}
return &Parameters{
modulusSizeBits: values.ModulusSizeBits,
sigHashType: values.SigHashType,
mgf1HashType: values.MGF1HashType,
publicExponent: values.PublicExponent,
saltLengthBytes: values.SaltLengthBytes,
variant: variant,
}, nil
}
// HasIDRequirement tells whether the key has an ID requirement.
func (p *Parameters) HasIDRequirement() bool { return p.variant != VariantNoPrefix }
// Equal tells whether this parameters object is equal to other.
func (p *Parameters) Equal(other key.Parameters) bool {
that, ok := other.(*Parameters)
return ok && p.HasIDRequirement() == that.HasIDRequirement() &&
p.modulusSizeBits == that.modulusSizeBits &&
p.sigHashType == that.sigHashType &&
p.mgf1HashType == that.mgf1HashType &&
p.publicExponent == that.publicExponent &&
p.saltLengthBytes == that.saltLengthBytes &&
p.variant == that.variant
}
// PublicKey represents a function that can verify RSA-SSA-PSS signatures
// as defined in [RFC 3447, Section 8.1].
type PublicKey struct {
modulus []byte // Big integer value in big-endian encoding.
idRequirement uint32
outputPrefix []byte
parameters *Parameters
}
var _ key.Key = (*PublicKey)(nil)
func calculateOutputPrefix(variant Variant, idRequirement uint32) ([]byte, error) {
switch variant {
case VariantTink:
return outputprefix.Tink(idRequirement), nil
case VariantCrunchy, VariantLegacy:
return outputprefix.Legacy(idRequirement), nil
case VariantNoPrefix:
return nil, nil
default:
return nil, fmt.Errorf("invalid output prefix variant: %v", variant)
}
}
// NewPublicKey creates a new RSA-SSA-PSS PublicKey object from modulus,
// ID requirement and parameters.
//
// modulus is a Big integer value in big-endian encoding. Parameters must be
// non-nil.
func NewPublicKey(modulus []byte, idRequirement uint32, parameters *Parameters) (*PublicKey, error) {
// This is set to UnknownHashType if the parameters is a struct literal.
if parameters.SigHashType() == UnknownHashType {
return nil, fmt.Errorf("rsassapss.NewPublicKey: invalid parameters")
}
modulusBigInt := new(big.Int).SetBytes(modulus)
if modulusBigInt.BitLen() != parameters.ModulusSizeBits() {
return nil, fmt.Errorf("rsassapss.NewPublicKey: invalid modulus bit-length: %v, want %v", modulusBigInt.BitLen(), parameters.ModulusSizeBits())
}
if parameters.Variant() == VariantNoPrefix && idRequirement != 0 {
return nil, fmt.Errorf("rsassapss.NewPublicKey: key ID must be zero for VariantNoPrefix")
}
outputPrefix, err := calculateOutputPrefix(parameters.Variant(), idRequirement)
if err != nil {
return nil, fmt.Errorf("rsassapss.NewPublicKey: %v", err)
}
return &PublicKey{
modulus: modulusBigInt.Bytes(),
idRequirement: idRequirement,
outputPrefix: outputPrefix,
parameters: parameters,
}, nil
}
// Modulus returns the public key modulus.
func (k *PublicKey) Modulus() []byte { return bytes.Clone(k.modulus) }
// Parameters returns the parameters of this key.
func (k *PublicKey) Parameters() key.Parameters { return k.parameters }
// IDRequirement returns the key ID requirement and whether it is required.
func (k *PublicKey) IDRequirement() (uint32, bool) {
return k.idRequirement, k.Parameters().HasIDRequirement()
}
// OutputPrefix returns the output prefix of this key.
func (k *PublicKey) OutputPrefix() []byte { return bytes.Clone(k.outputPrefix) }
// Equal tells whether this key object is equal to other.
func (k *PublicKey) Equal(other key.Key) bool {
actualKey, ok := other.(*PublicKey)
return ok && bytes.Equal(k.modulus, actualKey.modulus) &&
k.idRequirement == actualKey.idRequirement &&
k.parameters.Equal(actualKey.parameters)
}
// PrivateKey represents a function that can produce RSA-SSA-PSS
// signatures as defined in [RFC 3447, Section 8.1].
type PrivateKey struct {
publicKey *PublicKey
privateKey *rsa.PrivateKey
}
// PrivateKeyValues contains the values of a private key.
type PrivateKeyValues struct {
P, Q secretdata.Bytes
D secretdata.Bytes
// dp, dq and QInv must be computed by the Go library.
// See https://pkg.go.dev/crypto/rsa#PrivateKey.
}
// privateKeySelfCheck signs a test message with a private key and verifies a
// the signature with the corresponding public key.
//
// This is a security check to ensure that the private key is valid.
func privateKeySelfCheck(privateKey *PrivateKey) error {
signer, err := NewSigner(privateKey, internalapi.Token{})
if err != nil {
return err
}
verifier, err := NewVerifier(privateKey.publicKey, internalapi.Token{})
if err != nil {
return err
}
testMessage := []byte("Tink and Wycheproof.")
signature, err := signer.Sign(testMessage)
if err != nil {
return err
}
return verifier.Verify(signature, testMessage)
}
// NewPrivateKey creates a new RSA-SSA-PSS PrivateKey value from a public key
// and private key values.
//
// publicKey must be non-nil.
func NewPrivateKey(publicKey *PublicKey, opts PrivateKeyValues) (*PrivateKey, error) {
if publicKey.parameters == nil {
return nil, fmt.Errorf("rsassapss.NewPrivateKey: invalid public key")
}
privateKey := rsa.PrivateKey{
PublicKey: rsa.PublicKey{
N: new(big.Int).SetBytes(publicKey.Modulus()),
E: publicKey.parameters.PublicExponent(),
},
D: new(big.Int).SetBytes(opts.D.Data(insecuresecretdataaccess.Token{})),
Primes: []*big.Int{
new(big.Int).SetBytes(opts.P.Data(insecuresecretdataaccess.Token{})),
new(big.Int).SetBytes(opts.Q.Data(insecuresecretdataaccess.Token{})),
},
}
if err := privateKey.Validate(); err != nil {
return nil, fmt.Errorf("rsassapss.NewPrivateKey: %v", err)
}
privateKey.Precompute()
pk := &PrivateKey{
publicKey: publicKey,
privateKey: &privateKey,
}
if err := privateKeySelfCheck(pk); err != nil {
return nil, fmt.Errorf("rsassapss.NewPrivateKey: %v", err)
}
return pk, nil
}
// P returns the prime P.
func (k *PrivateKey) P() secretdata.Bytes {
return secretdata.NewBytesFromData(k.privateKey.Primes[0].Bytes(), insecuresecretdataaccess.Token{})
}
// Q returns the prime Q.
func (k *PrivateKey) Q() secretdata.Bytes {
return secretdata.NewBytesFromData(k.privateKey.Primes[1].Bytes(), insecuresecretdataaccess.Token{})
}
// D returns the private exponent D.
func (k *PrivateKey) D() secretdata.Bytes {
return secretdata.NewBytesFromData(k.privateKey.D.Bytes(), insecuresecretdataaccess.Token{})
}
// DP returns the private prime factor P-1.
func (k *PrivateKey) DP() secretdata.Bytes {
return secretdata.NewBytesFromData(k.privateKey.Precomputed.Dp.Bytes(), insecuresecretdataaccess.Token{})
}
// DQ returns the private prime factor Q-1.
func (k *PrivateKey) DQ() secretdata.Bytes {
return secretdata.NewBytesFromData(k.privateKey.Precomputed.Dq.Bytes(), insecuresecretdataaccess.Token{})
}
// QInv returns the inverse of Q.
func (k *PrivateKey) QInv() secretdata.Bytes {
return secretdata.NewBytesFromData(k.privateKey.Precomputed.Qinv.Bytes(), insecuresecretdataaccess.Token{})
}
// PublicKey returns the corresponding public key.
func (k *PrivateKey) PublicKey() (key.Key, error) { return k.publicKey, nil }
// Parameters returns the parameters of this key.
func (k *PrivateKey) Parameters() key.Parameters { return k.publicKey.Parameters() }
// IDRequirement tells whether the key ID and whether it is required.
func (k *PrivateKey) IDRequirement() (uint32, bool) { return k.publicKey.IDRequirement() }
// OutputPrefix returns the output prefix of this key.
func (k *PrivateKey) OutputPrefix() []byte { return k.publicKey.OutputPrefix() }
// Equal tells whether this key object is equal to other.
func (k *PrivateKey) Equal(other key.Key) bool {
that, ok := other.(*PrivateKey)
return ok && k.publicKey.Equal(that.publicKey) && k.privateKey.Equal(that.privateKey)
}
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