ConfidentialMPTConvert.cpp

#include <xrpl/tx/transactors/token/ConfidentialMPTConvert.h>
 
#include <xrpl/basics/Log.h>
#include <xrpl/basics/Slice.h>
#include <xrpl/beast/utility/Journal.h>
#include <xrpl/beast/utility/instrumentation.h>
#include <xrpl/core/ServiceRegistry.h>
#include <xrpl/ledger/ReadView.h>
#include <xrpl/ledger/helpers/TokenHelpers.h>
#include <xrpl/protocol/ConfidentialTransfer.h>
#include <xrpl/protocol/Indexes.h>
#include <xrpl/protocol/LedgerFormats.h>
#include <xrpl/protocol/MPTIssue.h>
#include <xrpl/protocol/Protocol.h>
#include <xrpl/protocol/SField.h>
#include <xrpl/protocol/TER.h>
#include <xrpl/protocol/XRPAmount.h>
#include <xrpl/tx/Transactor.h>
 
#include <memory>
#include <optional>
#include <utility>
 
namespace xrpl {
 
NotTEC
ConfidentialMPTConvert::preflight(PreflightContext const& ctx)
{
    // issuer cannot convert
    if (MPTIssue(ctx.tx[sfMPTokenIssuanceID]).getIssuer() == ctx.tx[sfAccount])
        return temMALFORMED;
 
    if (ctx.tx[sfMPTAmount] > kMaxMpTokenAmount)
        return temBAD_AMOUNT;
 
    if (ctx.tx.isFieldPresent(sfHolderEncryptionKey))
    {
        if (!isValidCompressedECPoint(ctx.tx[sfHolderEncryptionKey]))
            return temMALFORMED;
 
        // proof of knowledge of the secret key corresponding to the provided
        // public key is needed when holder ec public key is being set.
        if (!ctx.tx.isFieldPresent(sfZKProof))
            return temMALFORMED;
 
        // verify schnorr proof length when registering holder ec public key
        if (ctx.tx[sfZKProof].size() != kEcSchnorrProofLength)
            return temMALFORMED;
    }
    else
    {
        // Either both sfHolderEncryptionKey and sfZKProof should be present, or both should be
        // absent.
        if (ctx.tx.isFieldPresent(sfZKProof))
            return temMALFORMED;
    }
 
    // check encrypted amount format after the above basic checks
    // this check is more expensive so put it at the end
    if (auto const res = checkEncryptedAmountFormat(ctx.tx); !isTesSuccess(res))
        return res;
 
    return tesSUCCESS;
}
 
XRPAmount
ConfidentialMPTConvert::calculateBaseFee(ReadView const& view, STTx const& tx)
{
    return Transactor::calculateBaseFee(view, tx, kConfidentialFeeMultiplier);
}
 
TER
ConfidentialMPTConvert::preclaim(PreclaimContext const& ctx)
{
    auto const account = ctx.tx[sfAccount];
    auto const issuanceID = ctx.tx[sfMPTokenIssuanceID];
    auto const amount = ctx.tx[sfMPTAmount];
 
    // ensure that issuance exists
    auto const sleIssuance = ctx.view.read(keylet::mptokenIssuance(issuanceID));
    if (!sleIssuance)
        return tecOBJECT_NOT_FOUND;
 
    if (!sleIssuance->isFlag(lsfMPTCanHoldConfidentialBalance) ||
        !sleIssuance->isFieldPresent(sfIssuerEncryptionKey))
    {
        return tecNO_PERMISSION;
    }
 
    // already checked in preflight, but should also check that issuer on the
    // issuance isn't the account either
    if (sleIssuance->getAccountID(sfIssuer) == account)
    {
        // LCOV_EXCL_START
        UNREACHABLE(
            "xrpl::ConfidentialMPTConvert::preclaim : issuer derived from the MPT ID must "
            "match the ledger's stored issuer");
        return tefINTERNAL;
        // LCOV_EXCL_STOP
    }
 
    bool const hasAuditor = ctx.tx.isFieldPresent(sfAuditorEncryptedAmount);
    bool const requiresAuditor = sleIssuance->isFieldPresent(sfAuditorEncryptionKey);
 
    // tx must include auditor ciphertext if the issuance has enabled
    // auditing, and must not include it if auditing is not enabled
    if (requiresAuditor != hasAuditor)
        return tecNO_PERMISSION;
 
    auto const sleMptoken = ctx.view.read(keylet::mptoken(issuanceID, account));
    if (!sleMptoken)
        return tecOBJECT_NOT_FOUND;
 
    auto const mptIssue = MPTIssue{issuanceID};
 
    // Explicit freeze and auth checks are required because accountHolds
    // with ZeroIfFrozen/ZeroIfUnauthorized only implicitly rejects
    // non-zero amounts. A zero-amount convert would bypass those implicit
    // checks, allowing frozen or unauthorized accounts to register ElGamal
    // keys and initialize confidential balance fields.
 
    // Check lock
    if (auto const ter = checkFrozen(ctx.view, account, mptIssue); !isTesSuccess(ter))
        return ter;
 
    // Check auth
    if (auto const ter = requireAuth(ctx.view, mptIssue, account); !isTesSuccess(ter))
        return ter;
 
    auto const mptAmount =
        STAmount(MPTAmount{static_cast<MPTAmount::value_type>(amount)}, mptIssue);
    if (accountHolds(
            ctx.view,
            account,
            mptIssue,
            FreezeHandling::ZeroIfFrozen,
            AuthHandling::ZeroIfUnauthorized,
            ctx.j) < mptAmount)
    {
        return tecINSUFFICIENT_FUNDS;
    }
 
    auto const hasHolderKeyOnLedger = sleMptoken->isFieldPresent(sfHolderEncryptionKey);
    auto const hasHolderKeyInTx = ctx.tx.isFieldPresent(sfHolderEncryptionKey);
 
    // must have pk to convert
    if (!hasHolderKeyOnLedger && !hasHolderKeyInTx)
        return tecNO_PERMISSION;
 
    // can't update if there's already a pk
    if (hasHolderKeyOnLedger && hasHolderKeyInTx)
        return tecDUPLICATE;
 
    // Run all verifications before returning any error to prevent timing attacks
    // that could reveal which proof failed.
    bool valid = true;
 
    Slice holderPubKey;
    if (hasHolderKeyInTx)
    {
        holderPubKey = ctx.tx[sfHolderEncryptionKey];
 
        auto const contextHash =
            getConvertContextHash(account, issuanceID, ctx.tx.getSeqProxy().value());
 
        if (auto const ter = verifySchnorrProof(holderPubKey, ctx.tx[sfZKProof], contextHash);
            !isTesSuccess(ter))
        {
            valid = false;
        }
    }
    else
    {
        holderPubKey = (*sleMptoken)[sfHolderEncryptionKey];
    }
 
    std::optional<ConfidentialRecipient> auditor;
    if (hasAuditor)
    {
        auditor.emplace(
            ConfidentialRecipient{
                .publicKey = (*sleIssuance)[sfAuditorEncryptionKey],
                .encryptedAmount = ctx.tx[sfAuditorEncryptedAmount],
            });
    }
 
    auto const blindingFactor = ctx.tx[sfBlindingFactor];
    if (auto const ter = verifyRevealedAmount(
            amount,
            Slice(blindingFactor.data(), blindingFactor.size()),
            {
                .publicKey = holderPubKey,
                .encryptedAmount = ctx.tx[sfHolderEncryptedAmount],
            },
            {
                .publicKey = (*sleIssuance)[sfIssuerEncryptionKey],
                .encryptedAmount = ctx.tx[sfIssuerEncryptedAmount],
            },
            auditor);
        !isTesSuccess(ter))
    {
        valid = false;
    }
 
    if (!valid)
        return tecBAD_PROOF;
 
    return tesSUCCESS;
}
 
TER
ConfidentialMPTConvert::doApply()
{
    auto const mptIssuanceID = ctx_.tx[sfMPTokenIssuanceID];
 
    auto sleMptoken = view().peek(keylet::mptoken(mptIssuanceID, accountID_));
    if (!sleMptoken)
    {
        // LCOV_EXCL_START
        UNREACHABLE(
            "xrpl::ConfidentialMPTConvert::doApply : preclaim already validated the MPToken "
            "exists");
        return tecINTERNAL;
        // LCOV_EXCL_STOP
    }
 
    auto sleIssuance = view().peek(keylet::mptokenIssuance(mptIssuanceID));
    if (!sleIssuance)
    {
        // LCOV_EXCL_START
        UNREACHABLE(
            "xrpl::ConfidentialMPTConvert::doApply : preclaim already validated the issuance "
            "exists");
        return tecINTERNAL;
        // LCOV_EXCL_STOP
    }
 
    auto const amtToConvert = ctx_.tx[sfMPTAmount];
    auto const amt = (*sleMptoken)[~sfMPTAmount].valueOr(0);
 
    if (ctx_.tx.isFieldPresent(sfHolderEncryptionKey))
        (*sleMptoken)[sfHolderEncryptionKey] = ctx_.tx[sfHolderEncryptionKey];
 
    // Converting decreases regular balance and increases confidential outstanding.
    // The confidential outstanding tracks total tokens in confidential form globally.
    auto const currentCOA = (*sleIssuance)[~sfConfidentialOutstandingAmount].valueOr(0);
    if (amtToConvert > kMaxMpTokenAmount - currentCOA)
        return tecINTERNAL;  // LCOV_EXCL_LINE
 
    (*sleMptoken)[sfMPTAmount] = amt - amtToConvert;
    (*sleIssuance)[sfConfidentialOutstandingAmount] = currentCOA + amtToConvert;
 
    auto const holderEc = ctx_.tx[sfHolderEncryptedAmount];
    auto const issuerEc = ctx_.tx[sfIssuerEncryptedAmount];
    auto const auditorEc = ctx_.tx[~sfAuditorEncryptedAmount];
 
    // Two cases for Convert:
    // 1. Holder already has confidential balances -> homomorphically add to inbox
    // 2. First-time convert -> initialize all confidential balance fields
    if (sleMptoken->isFieldPresent(sfIssuerEncryptedBalance) &&
        sleMptoken->isFieldPresent(sfConfidentialBalanceInbox) &&
        sleMptoken->isFieldPresent(sfConfidentialBalanceSpending))
    {
        // Case 1: Add to existing inbox balance (holder will merge later)
        {
            auto sum = homomorphicAdd(holderEc, (*sleMptoken)[sfConfidentialBalanceInbox]);
            if (!sum)
            {
                // LCOV_EXCL_START
                JLOG(ctx_.journal.error())
                    << "ConfidentialMPTConvert failed homomorphic add for holder inbox.";
                return tecINTERNAL;
                // LCOV_EXCL_STOP
            }
 
            (*sleMptoken)[sfConfidentialBalanceInbox] = std::move(*sum);
        }
 
        // homomorphically add issuer's encrypted balance
        {
            auto sum = homomorphicAdd(issuerEc, (*sleMptoken)[sfIssuerEncryptedBalance]);
            if (!sum)
            {
                // LCOV_EXCL_START
                JLOG(ctx_.journal.error())
                    << "ConfidentialMPTConvert failed homomorphic add for issuer balance.";
                return tecINTERNAL;
                // LCOV_EXCL_STOP
            }
 
            (*sleMptoken)[sfIssuerEncryptedBalance] = std::move(*sum);
        }
 
        // homomorphically add auditor's encrypted balance
        if (auditorEc)
        {
            if (!sleMptoken->isFieldPresent(sfAuditorEncryptedBalance))
            {
                // LCOV_EXCL_START
                UNREACHABLE(
                    "xrpl::ConfidentialMPTConvert::doApply : issuance-level auditing implies "
                    "the MPToken already carries an auditor balance");
                return tecINTERNAL;
                // LCOV_EXCL_STOP
            }
 
            auto sum = homomorphicAdd(*auditorEc, (*sleMptoken)[sfAuditorEncryptedBalance]);
            if (!sum)
            {
                // LCOV_EXCL_START
                JLOG(ctx_.journal.error())
                    << "ConfidentialMPTConvert failed homomorphic add for auditor balance.";
                return tecINTERNAL;
                // LCOV_EXCL_STOP
            }
 
            (*sleMptoken)[sfAuditorEncryptedBalance] = std::move(*sum);
        }
    }
    else if (
        !sleMptoken->isFieldPresent(sfIssuerEncryptedBalance) &&
        !sleMptoken->isFieldPresent(sfConfidentialBalanceInbox) &&
        !sleMptoken->isFieldPresent(sfConfidentialBalanceSpending) &&
        !sleMptoken->isFieldPresent(sfAuditorEncryptedBalance))
    {
        // Case 2: First-time convert - initialize all confidential fields
        (*sleMptoken)[sfConfidentialBalanceInbox] = holderEc;
        (*sleMptoken)[sfIssuerEncryptedBalance] = issuerEc;
        (*sleMptoken)[sfConfidentialBalanceVersion] = 0;
 
        if (auditorEc)
            (*sleMptoken)[sfAuditorEncryptedBalance] = *auditorEc;
 
        // Spending balance starts at zero. Must use canonical zero encryption
        // (deterministic ciphertext) so the ledger state is reproducible.
        auto zeroBalance = encryptCanonicalZeroAmount(
            (*sleMptoken)[sfHolderEncryptionKey], accountID_, mptIssuanceID);
 
        if (!zeroBalance)
        {
            // LCOV_EXCL_START
            UNREACHABLE(
                "xrpl::ConfidentialMPTConvert::doApply : canonical zero encryption cannot fail "
                "for an already-valid holder public key");
            return tecINTERNAL;
            // LCOV_EXCL_STOP
        }
 
        (*sleMptoken)[sfConfidentialBalanceSpending] = std::move(*zeroBalance);
    }
    else
    {
        // both sfIssuerEncryptedBalance and sfConfidentialBalanceInbox should
        // exist together
        // LCOV_EXCL_START
        UNREACHABLE(
            "xrpl::ConfidentialMPTConvert::doApply : confidential balance fields must be all "
            "present or all absent");
        return tecINTERNAL;
        // LCOV_EXCL_STOP
    }
 
    view().update(sleIssuance);
    view().update(sleMptoken);
    return tesSUCCESS;
}
 
void
ConfidentialMPTConvert::visitInvariantEntry(
    bool,
    std::shared_ptr<SLE const> const&,
    std::shared_ptr<SLE const> const&)
{
}
 
bool
ConfidentialMPTConvert::finalizeInvariants(
    STTx const&,
    TER,
    XRPAmount,
    ReadView const&,
    beast::Journal const&)
{
    return true;
}
 
}  // namespace xrpl