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hpke: Enforces passing a slice of exact size to UnmarshalBinary for KEM keys #489

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hpke: Enforces passing a slice of exact size to UnmarshalBinary for KEM keys #489

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12ba47d
Test showing Issue #488, unmarshal keys panics.
armfazh Mar 13, 2024
df5ea67
Enforces passing slices of the exact size when unmarshaling KEM keys.
armfazh Mar 14, 2024
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63 changes: 63 additions & 0 deletions hpke/kem_test.go
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@@ -0,0 +1,63 @@
package hpke_test

import (
"fmt"
"testing"

"github.com/cloudflare/circl/hpke"
"github.com/cloudflare/circl/internal/test"
)

func TestKemKeysMarshal(t *testing.T) {
for _, kem := range []hpke.KEM{
hpke.KEM_P256_HKDF_SHA256,
hpke.KEM_P384_HKDF_SHA384,
hpke.KEM_P521_HKDF_SHA512,
hpke.KEM_X25519_HKDF_SHA256,
hpke.KEM_X448_HKDF_SHA512,
hpke.KEM_X25519_KYBER768_DRAFT00,
} {
checkIssue488(t, kem)
}
}

func checkIssue488(t *testing.T, kem hpke.KEM) {
scheme := kem.Scheme()
pk, sk, err := scheme.GenerateKeyPair()
if err != nil {
t.Fatal(err)
}
skBytes, err := sk.MarshalBinary()
test.CheckNoErr(t, err, "marshal private key")
pkBytes, err := pk.MarshalBinary()
test.CheckNoErr(t, err, "marshal public key")

t.Run(fmt.Sprintf("%v/PrivateKey", scheme.Name()), func(t *testing.T) {
N := scheme.PrivateKeySize()
buffer := make([]byte, N+1)
copy(buffer, skBytes)

// passing a buffer larger than the private key size should error (but no panic).
_, err := scheme.UnmarshalBinaryPrivateKey(buffer[:N+1])
test.CheckIsErr(t, err, "unmarshal private key should failed")

// passing a buffer of the exact size must be correct.
gotSk, err := scheme.UnmarshalBinaryPrivateKey(buffer[:N])
test.CheckNoErr(t, err, "unmarshal private key shouldn't fail")
test.CheckOk(sk.Equal(gotSk), "private keys are not equal", t)
})

t.Run(fmt.Sprintf("%v/PublicKey", scheme.Name()), func(t *testing.T) {
N := scheme.PublicKeySize()
buffer := make([]byte, N+1)
copy(buffer, pkBytes)

// passing a buffer larger than the public key size should error (but no panic).
_, err := scheme.UnmarshalBinaryPublicKey(buffer[:N+1])
test.CheckIsErr(t, err, "unmarshal public key should failed")

gotPk, err := scheme.UnmarshalBinaryPublicKey(buffer[:N])
test.CheckNoErr(t, err, "unmarshal public key shouldn't fail")
test.CheckOk(pk.Equal(gotPk), "public keys are not equal", t)
})
}
19 changes: 11 additions & 8 deletions hpke/shortkem.go
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Expand Up @@ -53,6 +53,7 @@ func (s shortKEM) DeriveKeyPair(seed []byte) (kem.PublicKey, kem.PrivateKey) {
bitmask = 0x01
}

Nsk := s.PrivateKeySize()
dkpPrk := s.labeledExtract([]byte(""), []byte("dkp_prk"), seed)
var bytes []byte
ctr := 0
Expand All @@ -64,14 +65,12 @@ func (s shortKEM) DeriveKeyPair(seed []byte) (kem.PublicKey, kem.PrivateKey) {
dkpPrk,
[]byte("candidate"),
[]byte{byte(ctr)},
uint16(s.byteSize()),
uint16(Nsk),
)
bytes[0] &= bitmask
skBig.SetBytes(bytes)
}
l := s.PrivateKeySize()
sk := &shortKEMPrivKey{s, make([]byte, l), nil}
copy(sk.priv[l-len(bytes):], bytes)
sk := &shortKEMPrivKey{s, bytes, nil}
return sk.Public(), sk
}

Expand All @@ -83,11 +82,11 @@ func (s shortKEM) GenerateKeyPair() (kem.PublicKey, kem.PrivateKey, error) {

func (s shortKEM) UnmarshalBinaryPrivateKey(data []byte) (kem.PrivateKey, error) {
l := s.PrivateKeySize()
if len(data) < l {
return nil, ErrInvalidKEMPrivateKey
if len(data) != l {
return nil, kem.ErrPrivKeySize
}
sk := &shortKEMPrivKey{s, make([]byte, l), nil}
copy(sk.priv[l-len(data):l], data[:l])
copy(sk.priv, data[:l])
if !sk.validate() {
return nil, ErrInvalidKEMPrivateKey
}
Expand All @@ -96,7 +95,11 @@ func (s shortKEM) UnmarshalBinaryPrivateKey(data []byte) (kem.PrivateKey, error)
}

func (s shortKEM) UnmarshalBinaryPublicKey(data []byte) (kem.PublicKey, error) {
x, y := elliptic.Unmarshal(s, data)
l := s.PublicKeySize()
if len(data) != l {
return nil, kem.ErrPubKeySize
}
x, y := elliptic.Unmarshal(s, data[:l])
if x == nil {
return nil, ErrInvalidKEMPublicKey
}
Expand Down
13 changes: 7 additions & 6 deletions hpke/xkem.go
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Expand Up @@ -58,13 +58,14 @@ func (x xKEM) DeriveKeyPair(seed []byte) (kem.PublicKey, kem.PrivateKey) {
if len(seed) != x.SeedSize() {
panic(kem.ErrSeedSize)
}
sk := &xKEMPrivKey{scheme: x, priv: make([]byte, x.size)}
Nsk := x.PrivateKeySize()
sk := &xKEMPrivKey{scheme: x, priv: make([]byte, Nsk)}
dkpPrk := x.labeledExtract([]byte(""), []byte("dkp_prk"), seed)
bytes := x.labeledExpand(
dkpPrk,
[]byte("sk"),
nil,
uint16(x.PrivateKeySize()),
uint16(Nsk),
)
copy(sk.priv, bytes)
return sk.Public(), sk
Expand All @@ -81,8 +82,8 @@ func (x xKEM) GenerateKeyPair() (kem.PublicKey, kem.PrivateKey, error) {

func (x xKEM) UnmarshalBinaryPrivateKey(data []byte) (kem.PrivateKey, error) {
l := x.PrivateKeySize()
if len(data) < l {
return nil, ErrInvalidKEMPrivateKey
if len(data) != l {
return nil, kem.ErrPrivKeySize
}
sk := &xKEMPrivKey{x, make([]byte, l), nil}
copy(sk.priv, data[:l])
Expand All @@ -94,8 +95,8 @@ func (x xKEM) UnmarshalBinaryPrivateKey(data []byte) (kem.PrivateKey, error) {

func (x xKEM) UnmarshalBinaryPublicKey(data []byte) (kem.PublicKey, error) {
l := x.PublicKeySize()
if len(data) < l {
return nil, ErrInvalidKEMPublicKey
if len(data) != l {
return nil, kem.ErrPubKeySize
}
pk := &xKEMPubKey{x, make([]byte, l)}
copy(pk.pub, data[:l])
Expand Down