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109 lines
2.0 KiB
Go
109 lines
2.0 KiB
Go
package mkem
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import (
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"github.com/henrydcase/nobs/dh/csidh"
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"github.com/henrydcase/nobs/drbg"
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"github.com/henrydcase/nobs/hash/sha3"
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)
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const (
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SharedSecretSz = 64
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PublicKeySz = 64
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)
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// Used for storing cipertext
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type ciphertext struct {
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// public key
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U [64]byte
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// private key
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V [64]byte
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}
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type PKE struct {
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Rng *drbg.CtrDrbg
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H sha3.ShakeHash
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}
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type MultiPKE struct {
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PKE
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// stores ephemeral/internal public key
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Ct0 [PublicKeySz]byte
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// stores list of ciphertexts ct[i]
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Cts [][SharedSecretSz]byte
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}
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// Allocates PKE
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func (c *PKE) Allocate(rng *drbg.CtrDrbg) {
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c.Rng = rng
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// Function H used in Algorithm 16 and 18
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c.H = sha3.NewShake128()
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}
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// Allocates MultiPKE
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func (c *MultiPKE) Allocate(recipients_nb uint, rng *drbg.CtrDrbg) {
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c.PKE.Allocate(rng)
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c.Cts = make([][SharedSecretSz]byte, recipients_nb)
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}
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// PKE encryption
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func (c *PKE) Enc(pk *csidh.PublicKey, pt *[16]byte) (ct ciphertext) {
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var ss [64]byte
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var pkA csidh.PublicKey
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var skA csidh.PrivateKey
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csidh.GeneratePrivateKey(&skA, c.Rng)
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csidh.DeriveSecret(&ss, pk, &skA, c.Rng)
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c.H.Reset()
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c.H.Write(ss[:])
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c.H.Read(ss[:16])
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for i := 0; i < 16; i++ {
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ct.V[i] = pt[i] ^ ss[i]
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}
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csidh.GeneratePublicKey(&pkA, &skA, c.Rng)
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pkA.Export(ct.U[:])
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return
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}
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// PKE decryption
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func (c *PKE) Dec(sk *csidh.PrivateKey, ct *ciphertext) (pt [16]byte) {
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var ss [64]byte
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var pk csidh.PublicKey
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pk.Import(ct.U[:])
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csidh.DeriveSecret(&ss, &pk, sk, c.Rng)
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c.H.Reset()
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c.H.Write(ss[:])
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c.H.Read(ss[:16])
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for i := 0; i < 16; i++ {
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pt[i] = ct.V[i] ^ ss[i]
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}
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return
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}
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// mPKE encryption
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func (c *MultiPKE) Encrypt(keys []csidh.PublicKey, pt *[16]byte) {
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var ss [64]byte
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var pkA csidh.PublicKey
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var skA csidh.PrivateKey
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csidh.GeneratePrivateKey(&skA, c.Rng)
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for i, pk := range keys {
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csidh.DeriveSecret(&ss, &pk, &skA, c.Rng)
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c.H.Write(ss[:])
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c.H.Read(ss[:16])
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c.H.Reset()
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for j := 0; j < 16; j++ {
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c.Cts[i][j] = pt[j] ^ ss[j]
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}
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}
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csidh.GeneratePublicKey(&pkA, &skA, c.Rng)
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pkA.Export(c.Ct0[:])
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return
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}
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