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Merge pull request #422 from JohnLCaron/decryptorErrors
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Decryptor uses ErrorMessages (no Exceptions).
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@JohnLCaron
JohnLCaron authored Nov 5, 2023
2 parents 948f097 + b9249e2 commit cbf2326
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Showing 20 changed files with 503 additions and 166 deletions.
20 changes: 12 additions & 8 deletions ...n/electionguard/decrypt/AllDecryptions.kt → ...tlin/electionguard/decrypt/Decryptions.kt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ data class PartialDecryption(

/** One selection decryption from one Decrypting Trustees. */
data class DecryptionResult(
val id: String, // "contestId#@selectionId" aka "selectionKey"
val selectionKey: String, // "contestId#@selectionId"
val ciphertext: ElGamalCiphertext, // text to decrypt
val share: PartialDecryption,
)
Expand Down Expand Up @@ -68,7 +68,7 @@ data class TrusteeChallengeResponses(
* Mutable, built incrementally.
*/
class DecryptionResults(
val selectionKey: String, // "contestId#@selectionId" aka "selectionKey"
val selectionKey: String, // "contestId#@selectionId"
val ciphertext: ElGamalCiphertext, // text to decrypt
val shares: MutableMap<String, PartialDecryption>, // key by guardianId
var tally: Int? = null, // the decrypted tally
Expand Down Expand Up @@ -108,11 +108,11 @@ class AllDecryptions {
}

/** add Partial decryptions from one DecryptingTrustee. */
fun addDecryption(guardianId: String, ciphertext: ElGamalCiphertext, decryption: PartialDecryption) {
var decryptionResults = shares[guardianId]
fun addDecryption(selectionKey: String, ciphertext: ElGamalCiphertext, decryption: PartialDecryption) {
var decryptionResults = shares[selectionKey]
if (decryptionResults == null) {
decryptionResults = DecryptionResults(guardianId, ciphertext, mutableMapOf())
shares[guardianId] = decryptionResults
decryptionResults = DecryptionResults(selectionKey, ciphertext, mutableMapOf())
shares[selectionKey] = decryptionResults
}
decryptionResults.shares[decryption.guardianId] = decryption
}
Expand All @@ -128,14 +128,18 @@ class AllDecryptions {
}

/** add challenge response from one DecryptingTrustee. */
fun addChallengeResponse(guardianId: String, cr : ChallengeResponse) {
fun addChallengeResponse(guardianId: String, cr : ChallengeResponse) : Boolean {
val dresult = shares[cr.id]
if (dresult != null) {
dresult.responses[guardianId] = cr.response
} else {
val cdresult = contestData[cr.id] ?: throw IllegalStateException("Cant find ${cr.id}")
val cdresult = contestData[cr.id]
if (cdresult == null) {
return false
}
cdresult.responses[guardianId] = cr.response
}
return true
}
}

Expand Down
80 changes: 51 additions & 29 deletions egklib/src/commonMain/kotlin/electionguard/decrypt/DecryptorDoerre.kt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@ package electionguard.decrypt
import electionguard.ballot.*
import electionguard.core.*
import electionguard.core.Base16.toHex
import electionguard.util.ErrorMessages
import electionguard.util.Stats

// TODO Use a configuration to set to the maximum possible vote. Keep low for testing to detect bugs quickly.
Expand Down Expand Up @@ -55,23 +56,23 @@ class DecryptorDoerre(
this.lagrangeCoordinates = dguardians.associateBy { it.guardianId }
}

fun decryptBallot(ballot: EncryptedBallot): DecryptedTallyOrBallot {
fun decryptBallot(ballot: EncryptedBallot, errs : ErrorMessages): DecryptedTallyOrBallot? {
// pretend a ballot is a tally
return ballot.convertToTally().decrypt(true)
return ballot.convertToTally().decrypt(errs,true)
}

fun decryptPep(ballot: EncryptedBallot): DecryptedTallyOrBallot {
return ballot.convertToTally().decrypt(isBallot = false, isPep = true)
fun decryptPep(ballot: EncryptedBallot, errs : ErrorMessages): DecryptedTallyOrBallot? {
return ballot.convertToTally().decrypt(errs, isBallot = false, isPep = true)
}

fun decryptPep(tally: EncryptedTally): DecryptedTallyOrBallot {
return tally.decrypt(isBallot = false, isPep = true)
fun decryptPep(tally: EncryptedTally, errs : ErrorMessages): DecryptedTallyOrBallot? {
return tally.decrypt(errs, isBallot = false, isPep = true)
}

var first = false
fun EncryptedTally.decrypt(isBallot : Boolean = false, isPep : Boolean = false): DecryptedTallyOrBallot {
fun EncryptedTally.decrypt(errs : ErrorMessages, isBallot : Boolean = false, isPep : Boolean = false): DecryptedTallyOrBallot? {
if (this.electionId != extendedBaseHash) {
throw RuntimeException("Encrypted Tally/Ballot has wrong electionId = ${this.electionId}")
errs.add("Encrypted Tally/Ballot has wrong electionId = ${this.electionId}")
}
val startDecrypt = getSystemTimeInMillis()
// must get the DecryptionResults from all trustees before we can do the challenges
Expand All @@ -91,18 +92,23 @@ class DecryptorDoerre(
// TODO if nguardians = 1, can set weightedProduct = Mi.
// lagrange weighted product of the shares, M = Prod(M_i^w_i) mod p; spec 2.0.0, eq 68
val weightedProduct = with(group) {
dresults.shares.map { (key, value) ->
val coeff = lagrangeCoordinates[key] ?: throw IllegalArgumentException()
value.Mi powP coeff.lagrangeCoefficient
dresults.shares.map { (guardianId, value) ->
val lagrange = lagrangeCoordinates[guardianId]
val coeff = if (lagrange == null) {
errs.add("missing lagrangeCoordinate for $guardianId")
group.ONE_MOD_Q
} else {
lagrange.lagrangeCoefficient
}
value.Mi powP coeff
}.multP()
}

// T = B · M−1 mod p; spec 2.0.0, eq 64
val T = dresults.ciphertext.data / weightedProduct
// T = K^t mod p, take log to get t = tally.
// Dont bother taking the log for PEP, it will not be found when (m1 != m2)), just test T == 1 for equality.
// TODO something better than exception ??
dresults.tally = if (isPep) 0 else jointPublicKey.dLog(T, maxDlog) ?: throw RuntimeException("dLog not found on $selectionKey")
dresults.tally = if (isPep) 0 else jointPublicKey.dLog(T, maxDlog) ?: errs.addNull("dLog not found on $selectionKey") as Int?
dresults.M = weightedProduct

// compute the collective challenge, needed for the collective proof; spec 2.0.0 eq 70
Expand Down Expand Up @@ -136,9 +142,15 @@ class DecryptorDoerre(
for (cresults in allDecryptions.contestData.values) {
// lagrange weighted product of the shares, beta = Prod(M_i^w_i) mod p; spec 2.0.0, eq 78
val weightedProduct = with(group) {
cresults.shares.map { (key, value) ->
val coeff = lagrangeCoordinates[key] ?: throw IllegalArgumentException()
value.Mi powP coeff.lagrangeCoefficient
cresults.shares.map { (guardianId, value) ->
val lagrange = lagrangeCoordinates[guardianId]
val coeff = if (lagrange == null) {
errs.add("missing lagrangeCoordinate for $guardianId")
group.ONE_MOD_Q
} else {
lagrange.lagrangeCoefficient
}
value.Mi powP coeff
}.multP()
}
cresults.beta = weightedProduct
Expand All @@ -161,11 +173,13 @@ class DecryptorDoerre(
val startChallengeCalls = getSystemTimeInMillis()
val trusteeChallengeResponses = mutableListOf<TrusteeChallengeResponses>()
for (trustee in decryptingTrustees) {
trusteeChallengeResponses.add(allDecryptions.challengeTrustee(trustee))
trusteeChallengeResponses.add(allDecryptions.challengeTrustee(trustee, errs.nested("trusteeChallengeResponses")))
}
trusteeChallengeResponses.forEach { challengeResponses ->
challengeResponses.results.forEach {
allDecryptions.addChallengeResponse(challengeResponses.id, it)
if (!allDecryptions.addChallengeResponse(challengeResponses.id, it)) {
errs.add("Cant find challengeResponse id='${challengeResponses.id}'")
}
}
}

Expand All @@ -176,10 +190,10 @@ class DecryptorDoerre(
// After gathering the challenge responses from the available trustees, we can verify and publish.
// Put that code into a different class to keep this one from getting too big.
val tallyDecryptor = TallyDecryptor(group, extendedBaseHash, jointPublicKey, lagrangeCoordinates, guardians)
val result = tallyDecryptor.decryptTally(this, allDecryptions, stats)
val result = tallyDecryptor.decryptTally(this, allDecryptions, stats, errs.nested("TallyDecryptor.decryptTally"))

stats.of("decryptTally").accum(getSystemTimeInMillis() - startTally, ndecrypt)
return result
return if (errs.hasErrors()) null else result!!
}

/**
Expand Down Expand Up @@ -223,22 +237,30 @@ class DecryptorDoerre(
}

// send all challenges for a ballot / tally to one trustee
fun AllDecryptions.challengeTrustee(trustee: DecryptingTrusteeIF) : TrusteeChallengeResponses {
fun AllDecryptions.challengeTrustee(trustee: DecryptingTrusteeIF, errs : ErrorMessages) : TrusteeChallengeResponses {
val wi = lagrangeCoordinates[trustee.id()]!!.lagrangeCoefficient
// Get all the challenges from the shares for this trustee
val requests: MutableList<ChallengeRequest> = mutableListOf()
for ((selectionKey, results) in this.shares) {
val result = results.shares[trustee.id()] ?: throw IllegalStateException("missing ${trustee.id()}")
// spec 2.0.0, eq 72
val ci = wi * results.collectiveChallenge!!.toElementModQ(group)
requests.add(ChallengeRequest(selectionKey, ci, result.u))
val result = results.shares[trustee.id()]
if (result == null) {
errs.add("missing share ${trustee.id()}")
} else {
// spec 2.0.0, eq 72
val ci = wi * results.collectiveChallenge!!.toElementModQ(group)
requests.add(ChallengeRequest(selectionKey, ci, result.u))
}
}
// Get all the challenges from the contestData
for ((id, results) in this.contestData) {
val result = results.shares[trustee.id()] ?: throw IllegalStateException("missing ${trustee.id()}")
// spec 2.0.0, eq 72
val ci = wi * results.collectiveChallenge!!.toElementModQ(group)
requests.add(ChallengeRequest(id, ci, result.u))
val result = results.shares[trustee.id()]
if (result == null) {
errs.add("missing contestData ${trustee.id()}")
} else {
// spec 2.0.0, eq 72
val ci = wi * results.collectiveChallenge!!.toElementModQ(group)
requests.add(ChallengeRequest(id, ci, result.u))
}
}

// ask for all of them at once from the trustee
Expand Down
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