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Code Issues Releases Wiki Activity

Comment re: AtE vs. EtA

This commit is contained in:
Russ Magee 2020-12-15 21:15:15 -08:00
parent 5f42894ac2
commit 640e59be4f
1 changed files with 29 additions and 16 deletions
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45
xsnet/net.go
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@ -427,13 +427,13 @@ func FrodoKEMDialSetup(c io.ReadWriter, hc *Conn) (err error) {
}
pubA, secA := kem.Keygen() // pA
//log.Printf("[pubKeyAlice: %v]\n", pubA)
// Alice, step 2: Send the public key (na,ea) to Bob
fmt.Fprintf(c, "0x%x\n", pubA)
// (... and cipher, connection opts)
fmt.Fprintf(c, "0x%x:0x%x\n", hc.cipheropts, hc.opts)
// [Bob does the same and sends use a public key (nb, eb)
pubB_bigint := big.NewInt(0)
_, err = fmt.Fscanf(c, "0x%x\n", pubB_bigint)
@ -446,27 +446,27 @@ func FrodoKEMDialSetup(c io.ReadWriter, hc *Conn) (err error) {
if err != nil {
return err
}
// Alice, step 3: Create ctAtoB, shareA
ctAtoB, shareA, err := kem.Encapsulate(pubB)
if err != nil {
return err
}
// Alice, step 4: Send ctAtoB to Bob
fmt.Fprintf(c, "0x%x\n", ctAtoB)
// Alice, step 5: Receive ctBtoA from Bob
ctBtoA_bigint := big.NewInt(0)
_, err = fmt.Fscanf(c, "0x%x\n", ctBtoA_bigint)
ctBtoA := ctBtoA_bigint.Bytes()
log.Printf("[Got ctBob[]:%v]\n", ctBtoA)
// Alice, step 6: compute Bob's share
shareB, err := kem.Dencapsulate(secA, ctBtoA)
sessionKey := append(shareA, shareB...)
//log.Printf("[Derived sharedSecret:0x%x]\n", sessionKey)
hc.r, hc.rm, err = hc.getStream(sessionKey)
hc.w, hc.wm, err = hc.getStream(sessionKey)
return
@ -681,13 +681,13 @@ func FrodoKEMAcceptSetup(c *net.Conn, hc *Conn) (err error) {
}
pubB, secB := kem.Keygen()
//log.Printf("[pubKeyBob: %v]\n", pubB)
// Bob, step 2: Send the public key (nb,eb) to Alice
fmt.Fprintf(*c, "0x%x\n", pubB)
// (... and cipher, connection opts)
fmt.Fprintf(*c, "0x%x:0x%x\n", hc.cipheropts, hc.opts)
// [Alice does the same and sends use a public key (na, ea)
pubA_bigint := big.NewInt(0)
_, err = fmt.Fscanf(*c, "0x%x\n", pubA_bigint)
@ -700,27 +700,27 @@ func FrodoKEMAcceptSetup(c *net.Conn, hc *Conn) (err error) {
if err != nil {
return err
}
// Bob, step 3: Create ctBtoA, shareB
ctBtoA, shareB, err := kem.Encapsulate(pubA)
if err != nil {
return err
}
// Bob, step 4: Send ctBtoA to Alice
fmt.Fprintf(*c, "0x%x\n", ctBtoA)
// Bob, step 5: Receive ctAtoB from Alice
ctAtoB_bigint := big.NewInt(0)
_, err = fmt.Fscanf(*c, "0x%x\n", ctAtoB_bigint)
ctAtoB := ctAtoB_bigint.Bytes()
log.Printf("[Got ctAlice[]:%v]\n", ctAtoB)
// Alice, step 6: compute Bob's share
shareA, err := kem.Dencapsulate(secB, ctAtoB)
sessionKey := append(shareA, shareB...)
//log.Printf("[Derived sharedSecret:0x%x]\n", sessionKey)
hc.r, hc.rm, err = hc.getStream(sessionKey)
hc.w, hc.wm, err = hc.getStream(sessionKey)
return
@ -1501,6 +1501,19 @@ func (hc *Conn) WritePacket(b []byte, ctrlStatOp byte) (n int, err error) {
log.Printf(" :>ptext:\r\n%s\r\n", hex.Dump(b[0:payloadLen]))
}
// NOTE the code currently uses Authenticate-then-Encrypt, which in block modes
// is insecure; however
// 1) we are using exclusively XOR-stream modes with random padding,
// 2) are padding randomly either before or after the real payload, and
// 3) the padding side indicator value itself is part of the ciphertext
// ... thus are not subject to oracle attacks of the type used on SSL
// (see https://link.springer.com/content/pdf/10.1007%2F3-540-44647-8_19.pdf)
//
// Nevertheless, to address any future concerns this code may switch to
// Encrypt-then-Auth and offer the current scheme as a legacy mode
// (or just issue a breaking release since this is very pre-1.0.)
// -rlm 2020-12-15
// Calculate hmac on payload
hc.wm.Write(b[0:payloadLen])
hmacOut = hc.wm.Sum(nil)[0:HMAC_CHK_SZ]