Identity-based encryption features to support timelock encryption

encrypt/ibe/ibe.go

@@ -0,0 +1,194 @@
+package ibe
+
+import (
+	"crypto/rand"
+	"errors"
+	"fmt"
+
+	"golang.org/x/crypto/blake2s"
+
+	"github.com/drand/kyber"
+	"github.com/drand/kyber/pairing"
+	"github.com/drand/kyber/util/random"
+)
+
+type Ciphertext struct {
+	// Random point rP
+	U kyber.Point
+	// Sigma attached to ID: sigma XOR H(rG_id)
+	V []byte
+	// ciphertext of the message M XOR H(sigma)
+	W []byte
+}
+
+// H2Tag is the domain separation tag for the H2 hash function
+func H2Tag() []byte {
+	return []byte("IBE-H2")
+}
+
+// H3Tag is the domain separation tag for the H3 hash function
+func H3Tag() []byte {
+	return []byte("IBE-H3")
+}
+
+// H4Tag is the domain separation tag for the H4 hash function
+func H4Tag() []byte {
+	return []byte("IBE-H4")
+}
+
+// Encrypt implements the cca identity based encryption scheme from
+// https://crypto.stanford.edu/~dabo/pubs/papers/bfibe.pdf for more information
+// about the scheme.
+// - master is the master key on G1
+// - ID is the ID towards which we encrypt the message
+// - msg is the actual message
+// - seed is the random seed to generate the random element (sigma) of the encryption
+// The suite must produce points which implements the `HashablePoint` interface.
+func Encrypt(s pairing.Suite, master kyber.Point, ID, msg []byte) (*Ciphertext, error) {
+	if len(msg)>>16 > 0 {
+		// we're using blake2 as XOF which only outputs 2^16-1 length
+		return nil, errors.New("plaintext too long for blake2")
+	}
+	// 1. Compute Gid = e(master,Q_id)
+	hG2, ok := s.G2().Point().(kyber.HashablePoint)
+	if !ok {
+		return nil, errors.New("point needs to implement `kyber.HashablePoint`")
+	}
+	Qid := hG2.Hash(ID)
+	Gid := s.Pair(master, Qid)
+
+	// 2. Derive random sigma
+	sigma := make([]byte, len(msg))
+	if _, err := rand.Read(sigma); err != nil {
+		return nil, fmt.Errorf("err reading rand sigma: %v", err)
+	}
+	// 3. Derive r from sigma and msg
+	r, err := h3(s, sigma, msg)
+	if err != nil {
+		return nil, err
+	}
+	// 4. Compute U = rP
+	U := s.G1().Point().Mul(r, s.G1().Point().Base())
+
+	// 5. Compute V = sigma XOR H2(rGid)
+	rGid := Gid.Mul(r, Gid) // even in Gt, it's additive notation
+	hrGid, err := gtToHash(rGid, len(msg), H2Tag())
+	if err != nil {
+		return nil, err
+	}
+	V := xor(sigma, hrGid)
+
+	// 6. Compute M XOR H(sigma)
+	hsigma, err := h4(sigma, len(msg))
+	if err != nil {
+		return nil, err
+	}
+	W := xor(msg, hsigma)
+
+	return &Ciphertext{
+		U: U,
+		V: V,
+		W: W,
+	}, nil
+}
+
+func Decrypt(s pairing.Suite, master, private kyber.Point, c *Ciphertext) ([]byte, error) {
+	// 1. Compute sigma = V XOR H2(e(rP,private))
+	gidt := s.Pair(c.U, private)
+	return subdecrypt(s, c, gidt)
+}
+
+func subdecrypt(s pairing.Suite, c *Ciphertext, gidt kyber.Point) ([]byte, error) {
+	hgidt, err := gtToHash(gidt, len(c.W), H2Tag())
+	if err != nil {
+		return nil, err
+	}
+	if len(hgidt) != len(c.V) {
+		return nil, fmt.Errorf("XorSigma is of invalid length: exp %d vs got %d", len(hgidt), len(c.V))
+	}
+	sigma := xor(hgidt, c.V)
+
+	// 2. Compute M = W XOR H4(sigma)
+	// but maybe simpler/better to put the length in the ciphertext
+	hsigma, err := h4(sigma, len(c.W))
+	if err != nil {
+		return nil, err
+	}
+
+	msg := xor(hsigma, c.W)
+
+	// 3. Check U = rP
+	r, err := h3(s, sigma, msg)
+	if err != nil {
+		return nil, err
+	}
+	rP := s.G1().Point().Mul(r, s.G1().Point().Base())
+	if !rP.Equal(c.U) {
+		return nil, fmt.Errorf("invalid proof: rP check failed")
+	}
+	return msg, nil
+
+}
+
+const maxSize = 1 << 10
+
+// hash sigma and msg to get r
+func h3(s pairing.Suite, sigma, msg []byte) (kyber.Scalar, error) {
+	h3, err := blake2s.NewXOF(maxSize, nil)
+	if err != nil {
+		panic(err)
+	}
+	if _, err := h3.Write(H3Tag()); err != nil {
+		return nil, fmt.Errorf("err hashing h3 tag: %v", err)
+	}
+	if _, err := h3.Write(sigma); err != nil {
+		return nil, fmt.Errorf("err hashing sigma to XOF: %v", err)
+	}
+	_, _ = h3.Write(msg)
+	return s.G1().Scalar().Pick(random.New(h3)), nil
+}
+
+func h4(sigma []byte, length int) ([]byte, error) {
+	h4, err := blake2s.NewXOF(maxSize, nil)
+	if err != nil {
+		panic(err)
+	}
+	if _, err := h4.Write(H4Tag()); err != nil {
+		return nil, fmt.Errorf("err writing h4tag: %v", err)
+	}
+	if _, err := h4.Write(sigma); err != nil {
+		return nil, fmt.Errorf("err writing sigma to h4: %v", err)
+	}
+	h4sigma := make([]byte, length)
+	if _, err := h4.Read(h4sigma); err != nil {
+		return nil, fmt.Errorf("err reading from h4: %v", err)
+	}
+	return h4sigma, nil
+}
+
+func gtToHash(gt kyber.Point, length int, dst []byte) ([]byte, error) {
+	xof, err := blake2s.NewXOF(maxSize, nil)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := xof.Write(dst); err != nil {
+		return nil, errors.New("err writing dst to gtHash")
+	}
+	gt.MarshalTo(xof)
+	var b = make([]byte, length)
+	if _, err := xof.Read(b); err != nil {
+		return nil, errors.New("couldn't read from xof")
+	}
+	return b[:], nil
+}
+
+func xor(a, b []byte) []byte {
+	if len(a) != len(b) {
+		panic("wrong xor input")
+	}
+	res := make([]byte, len(a))
+	for i := 0; i < len(a); i++ {
+		res[i] = a[i] ^ b[i]
+	}
+	return res
+}

encrypt/ibe/ibe_test.go

@@ -0,0 +1,56 @@
+package ibe
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/drand/kyber"
+	bls "github.com/drand/kyber-bls12381"
+	"github.com/drand/kyber/pairing"
+	"github.com/drand/kyber/util/random"
+	"github.com/stretchr/testify/require"
+)
+
+func newSetting() (pairing.Suite, kyber.Point, []byte, kyber.Point) {
+	suite := bls.NewBLS12381Suite()
+	P := suite.G1().Point().Base()
+	s := suite.G1().Scalar().Pick(random.New())
+	Ppub := suite.G1().Point().Mul(s, P)
+
+	ID := []byte("passtherand")
+	IDP := suite.G2().Point().(kyber.HashablePoint)
+	Qid := IDP.Hash(ID)     // public key
+	sQid := Qid.Mul(s, Qid) // secret key
+	return suite, Ppub, ID, sQid
+}
+
+func TestTimelock(t *testing.T) {
+	suite, Ppub, ID, sQid := newSetting()
+	msg := []byte("Hello World\n")
+
+	c, err := Encrypt(suite, Ppub, ID, msg)
+	require.NoError(t, err)
+	msg2, err := Decrypt(suite, Ppub, sQid, c)
+	require.NoError(t, err)
+	require.Equal(t, msg, msg2)
+}
+
+func TestVeryLongInputFailsEncryption(t *testing.T) {
+	suite, Ppub, ID, _ := newSetting()
+	msg := []byte(strings.Repeat("And you have to understand this, that a prince, especially a new one, cannot observe all those things for which men are esteemed", 1000))
+	_, err := Encrypt(suite, Ppub, ID, msg)
+	require.Error(t, err)
+}
+
+func TestVeryLongCipherFailsDecryptionBecauseOfLength(t *testing.T) {
+	suite, Ppub, ID, sQid := newSetting()
+	msg := []byte("hello world")
+	c, err := Encrypt(suite, Ppub, ID, msg)
+	require.NoError(t, err)
+
+	c.W = []byte(strings.Repeat("And you have to understand this, that a prince, especially a new one, cannot observe all those things for which men are esteemed", 1000))
+	_, err = Decrypt(suite, Ppub, sQid, c)
+
+	require.Error(t, err)
+	require.ErrorContains(t, err, "XorSigma is of invalid length")
+}

go.mod

@@ -1,13 +1,21 @@
 module github.com/drand/kyber
 
-go 1.13
+go 1.17
 
 require (
-	github.com/drand/kyber-bls12381 v0.2.1
-	github.com/jonboulle/clockwork v0.1.0
-	github.com/stretchr/testify v1.4.0
+	github.com/drand/kyber-bls12381 v0.2.2
+	github.com/jonboulle/clockwork v0.3.0
+	github.com/stretchr/testify v1.7.2
 	go.dedis.ch/fixbuf v1.0.3
 	go.dedis.ch/protobuf v1.0.11
-	golang.org/x/crypto v0.0.0-20200820211705-5c72a883971a
-	golang.org/x/sys v0.0.0-20200926100807-9d91bd62050c
+	golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e
+	golang.org/x/sys v0.0.0-20220615213510-4f61da869c0c
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/kilic/bls12-381 v0.1.0 // indirect
+	github.com/kr/pretty v0.2.0 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -1,35 +1,36 @@
-github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/drand/bls12-381 v0.3.2 h1:RImU8Wckmx8XQx1tp1q04OV73J9Tj6mmpQLYDP7V1XE=
 github.com/drand/bls12-381 v0.3.2/go.mod h1:dtcLgPtYT38L3NO6mPDYH0nbpc5tjPassDqiniuAt4Y=
 github.com/drand/kyber v1.0.1-0.20200110225416-8de27ed8c0e2/go.mod h1:UpXoA0Upd1N9l4TvRPHr1qAUBBERj6JQ/mnKI3BPEmw=
 github.com/drand/kyber v1.0.2/go.mod h1:x6KOpK7avKj0GJ4emhXFP5n7M7W7ChAPmnQh/OL6vRw=
 github.com/drand/kyber v1.1.4/go.mod h1:9+IgTq7kadePhZg7eRwSD7+bA+bmvqRK+8DtmoV5a3U=
-github.com/drand/kyber-bls12381 v0.2.0 h1:3GJfiHaMggQS2l2n7yrfX0PjY9BYikLM2f0zKP1eZTs=
+github.com/drand/kyber v1.1.10/go.mod h1:UkHLsI4W6+jT5PvNxmc0cvQAgppjTUpX+XCsN9TXmRo=
 github.com/drand/kyber-bls12381 v0.2.0/go.mod h1:zQip/bHdeEB6HFZSU3v+d3cQE0GaBVQw9aR2E7AdoeI=
-github.com/drand/kyber-bls12381 v0.2.1 h1:/d5/YAdaCmHpYjF1NZevOEcKGaq6LBbyvkCTIdGqDjs=
 github.com/drand/kyber-bls12381 v0.2.1/go.mod h1:JwWn4nHO9Mp4F5qCie5sVIPQZ0X6cw8XAeMRvc/GXBE=
-github.com/jonboulle/clockwork v0.1.0 h1:VKV+ZcuP6l3yW9doeqz6ziZGgcynBVQO+obU0+0hcPo=
+github.com/drand/kyber-bls12381 v0.2.2 h1:MsqhbRUNIziZVGg5nT/AgZFXjKSc4Vd8jkBC0Y0sq4c=
+github.com/drand/kyber-bls12381 v0.2.2/go.mod h1:FsudUZf6Xu61u/gYrDHEHf6lKIKluJdnX7WJe4hkMh4=
 github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
-github.com/kilic/bls12-381 v0.0.0-20200607163746-32e1441c8a9f h1:qET3Wx0v8tMtoTOQnsJXVvqvCopSf48qobR6tcJuDHo=
+github.com/jonboulle/clockwork v0.3.0 h1:9BSCMi8C+0qdApAp4auwX0RkLGUjs956h0EkuQymUhg=
+github.com/jonboulle/clockwork v0.3.0/go.mod h1:Pkfl5aHPm1nk2H9h0bjmnJD/BcgbGXUBGnn1kMkgxc8=
 github.com/kilic/bls12-381 v0.0.0-20200607163746-32e1441c8a9f/go.mod h1:XXfR6YFCRSrkEXbNlIyDsgXVNJWVUV30m/ebkVy9n6s=
-github.com/kilic/bls12-381 v0.0.0-20200731194930-64c428e1bff5 h1:RAGCvOaqSiey3BGHopL/JI6+baO7D7AYQVDb6I8pRTs=
 github.com/kilic/bls12-381 v0.0.0-20200731194930-64c428e1bff5/go.mod h1:XXfR6YFCRSrkEXbNlIyDsgXVNJWVUV30m/ebkVy9n6s=
-github.com/kilic/bls12-381 v0.0.0-20200820230200-6b2c19996391 h1:51kHw7l/dUDdOdW06AlUGT5jnpj6nqQSILebcsikSjA=
 github.com/kilic/bls12-381 v0.0.0-20200820230200-6b2c19996391/go.mod h1:XXfR6YFCRSrkEXbNlIyDsgXVNJWVUV30m/ebkVy9n6s=
-github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
+github.com/kilic/bls12-381 v0.1.0 h1:encrdjqKMEvabVQ7qYOKu1OvhqpK4s47wDYtNiPtlp4=
+github.com/kilic/bls12-381 v0.1.0/go.mod h1:vDTTHJONJ6G+P2R74EhnyotQDTliQDnFEwhdmfzw1ig=
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+github.com/kr/pretty v0.2.0 h1:s5hAObm+yFO5uHYt5dYjxi2rXrsnmRpJx4OYvIWUaQs=
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 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
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 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
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 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
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 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
-github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.2 h1:4jaiDzPyXQvSd7D0EjG45355tLlV3VOECpq10pLC+8s=
+github.com/stretchr/testify v1.7.2/go.mod h1:R6va5+xMeoiuVRoj+gSkQ7d3FALtqAAGI1FQKckRals=
 go.dedis.ch/fixbuf v1.0.3 h1:hGcV9Cd/znUxlusJ64eAlExS+5cJDIyTyEG+otu5wQs=
 go.dedis.ch/fixbuf v1.0.3/go.mod h1:yzJMt34Wa5xD37V5RTdmp38cz3QhMagdGoem9anUalw=
 go.dedis.ch/kyber/v3 v3.0.4/go.mod h1:OzvaEnPvKlyrWyp3kGXlFdp7ap1VC6RkZDTaPikqhsQ=
@@ -42,33 +43,37 @@ go.dedis.ch/protobuf v1.0.11/go.mod h1:97QR256dnkimeNdfmURz0wAMNVbd1VmLXhG1CrTYr
 golang.org/x/crypto v0.0.0-20190123085648-057139ce5d2b/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
-golang.org/x/crypto v0.0.0-20200128174031-69ecbb4d6d5d h1:9FCpayM9Egr1baVnV1SX0H87m+XB0B8S0hAMi99X/3U=
 golang.org/x/crypto v0.0.0-20200128174031-69ecbb4d6d5d/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9 h1:vEg9joUBmeBcK9iSJftGNf3coIG4HqZElCPehJsfAYM=
 golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.0.0-20200728195943-123391ffb6de h1:ikNHVSjEfnvz6sxdSPCaPt572qowuyMDMJLLm3Db3ig=
 golang.org/x/crypto v0.0.0-20200728195943-123391ffb6de/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
-golang.org/x/crypto v0.0.0-20200820211705-5c72a883971a h1:vclmkQCjlDX5OydZ9wv8rBCcS0QyQY66Mpf/7BZbInM=
 golang.org/x/crypto v0.0.0-20200820211705-5c72a883971a/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e h1:T8NU3HyQ8ClP4SEE+KbFlg6n0NhuTsN4MyznaarGsZM=
+golang.org/x/crypto v0.0.0-20220525230936-793ad666bf5e/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
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 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
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-golang.org/x/sys v0.0.0-20200124204421-9fbb57f87de9 h1:1/DFK4b7JH8DmkqhUk48onnSfrPzImPoVxuomtbT2nk=
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hash.go

@@ -1,8 +1,15 @@
 package kyber
 
-import "hash"
+import (
+	"hash"
+)
 
 // A HashFactory is an interface that can be mixed in to local suite definitions.
 type HashFactory interface {
 	Hash() hash.Hash
 }
+
+// HashablePoint is an interface implemented by n
+type HashablePoint interface {
+	Hash([]byte) Point
+}