github.com/ronperry/cryptoedge@v0.0.0-20150815114006-cc363e290743/singhdas/signer.go (about)

     1  package singhdas
     2  
     3  import (
     4  	"github.com/ronperry/cryptoedge/eccutil"
     5  	"math/big"
     6  )
     7  
     8  // Signer is a signer instance
     9  type Signer struct {
    10  	privkey *big.Int
    11  	pubkey  *eccutil.Point
    12  	curve   *eccutil.Curve
    13  }
    14  
    15  // SignParamsInt encapsulates a single signature temporary key
    16  type SignParamsInt struct {
    17  	k    *big.Int       // Private, never share
    18  	Q    *eccutil.Point // Public, given to requestor
    19  	r    *big.Int
    20  	used bool // Never use twice
    21  }
    22  
    23  // BlindSignatureInt represents a single blind signature
    24  type BlindSignatureInt struct {
    25  	SignerBlind *eccutil.Point
    26  	S           *big.Int
    27  }
    28  
    29  // NewSigner returns a new signer
    30  func NewSigner(privkey []byte, pubkey *eccutil.Point, curve *eccutil.Curve) *Signer {
    31  	s := new(Signer)
    32  	s.privkey = new(big.Int)
    33  	s.privkey = s.privkey.SetBytes(privkey)
    34  	s.pubkey = pubkey
    35  	s.curve = curve
    36  	return s
    37  }
    38  
    39  // NewRequest issues a new request keypair
    40  func (signer Signer) NewRequest() (signparams *SignParamsInt, err error) {
    41  	var loopcount int
    42  	for {
    43  		if loopcount > eccutil.MaxLoopCount {
    44  			return nil, eccutil.ErrMaxLoop
    45  		}
    46  		loopcount++
    47  		Kt, Qt, err := signer.curve.GenerateKey()
    48  		if err != nil {
    49  			continue
    50  		}
    51  		r, err := signer.curve.ExtractR(Qt)
    52  		if err != nil {
    53  			continue
    54  		}
    55  		if !signer.curve.WithinRange(r) {
    56  			continue
    57  		}
    58  		sp := new(SignParamsInt)
    59  		sp.k = eccutil.BytesToInt(Kt)
    60  		sp.Q = Qt
    61  		sp.r = r
    62  		sp.used = false
    63  		return sp, nil
    64  	}
    65  }
    66  
    67  // Sign signs a blinded message
    68  func (signer Signer) Sign(blindMessage *BlindMessageInt, signParams *SignParamsInt) (S *BlindSignatureInt, err error) {
    69  	//signer.privkey * signParams.r + signParams.k * blindMessage.Message mod p
    70  	if signParams.used {
    71  		return nil, eccutil.ErrParamReuse
    72  	}
    73  	_, err = signer.curve.TestParams(blindMessage.Message, signer.privkey, signParams.r, signParams.k)
    74  	if err != nil {
    75  		return nil, eccutil.ErrBadBlindParam
    76  	}
    77  
    78  	Ar1 := eccutil.ManyMult(signer.privkey, signParams.r)
    79  	Km := eccutil.ManyMult(signParams.k, blindMessage.Message)
    80  	St := eccutil.ManyAdd(Ar1, Km)
    81  	Sm := signer.curve.Mod(St)
    82  	signParams.used = true
    83  	S = new(BlindSignatureInt)
    84  	S.S = Sm
    85  	S.SignerBlind = blindMessage.SignerBlind
    86  	return S, nil
    87  }