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[Security] Add challenge-response auth with scrypt verifiers and stop storing plaintext passwords

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Challenge-response authentication: the client derives a scrypt verifier
(RFC 7914, EVP_PBE_scrypt, N=32768, r=8, p=1) and authenticates with
HMAC-SHA256(key, nonce), so neither the password nor its hash is
transmitted. The stored format becomes
"$scrypt$<n>$<r>$<p>$<salt>$<verifier>" and Response_PasswordSalt
now carries the cost parameters. Strict servers only accept scrypt
verifiers; legacy accounts are migrated after a successful login.

Fix #344 for challenge-response servers: a saved profile stores the
derived verifier under the password key instead of the plaintext password.
The connect dialog loads it without revealing it, autoconnect passes it
through, the change-password dialog no longer prefills the old password
field with it, and the client only persists the verifier when
"Save password" is checked.

Took 3 minutes


Took 1 minute

Took 10 seconds
This commit is contained in:
Lukas Brübach 2026-08-04 11:36:10 +02:00
parent 5257a8bfa8
commit 088e932882
33 changed files with 675 additions and 23 deletions
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76
servatrice/src/servatrice_database_interface.cpp
View file

@ -354,6 +354,41 @@ AuthenticationResult Servatrice_DatabaseInterface::checkUserPassword(Server_Prot
qCWarning(DatabaseInterfaceLog) << "Login denied: user not active";
return UserIsInactive;
}
if (password.startsWith("$challenge$")) {
// Challenge-response login: verify HMAC(stored_key, nonce) without
// ever transmitting the stored credential or password hash.
const QStringList parts = password.split("$");
if (parts.size() != 4) {
return NotLoggedIn;
}
const QByteArray nonce = QByteArray::fromBase64(parts.at(2).toUtf8());
const QByteArray response = QByteArray::fromBase64(parts.at(3).toUtf8());
if (nonce.isEmpty() || response.isEmpty() || !handler->isAuthNonceValid(nonce)) {
return NotLoggedIn;
}
QByteArray key;
if (PasswordHasher::isLegacyFormat(correctPasswordSha512)) {
key = correctPasswordSha512.toUtf8();
} else {
const PasswordVerifier verifier = PasswordHasher::parsePasswordVerifier(correctPasswordSha512);
if (!verifier.isValid) {
return NotLoggedIn;
}
key = verifier.verifier;
}
const QByteArray expected = PasswordHasher::computeResponse(key, nonce);
handler->clearAuthNonce();
if (PasswordHasher::constantTimeEquals(expected, response)) {
qCDebug(DatabaseInterfaceLog) << "Login accepted: challenge-response password right";
return PasswordRight;
}
qCDebug(DatabaseInterfaceLog) << "Login denied: challenge-response password wrong";
return NotLoggedIn;
}
QString hashedPassword;
if (passwordNeedsHash) {
hashedPassword = PasswordHasher::computeHash(password, correctPasswordSha512.left(16));
@ -552,6 +587,47 @@ QString Servatrice_DatabaseInterface::getUserSalt(const QString &user)
return {};
}
QString Servatrice_DatabaseInterface::getUserPasswordData(const QString &user)
{
if (server->getAuthenticationMethod() != Servatrice::AuthenticationSql) {
return {};
}
checkSql();
QSqlQuery *query = prepareQuery("SELECT password_sha512 FROM {prefix}_users WHERE name = :name");
query->bindValue(":name", user);
if (!execSqlQuery(query)) {
return {};
}
if (!query->next()) {
return {};
}
return query->value(0).toString();
}
bool Servatrice_DatabaseInterface::submitPasswordVerifier(const QString &user, const QString &passwordVerifier)
{
if (server->getAuthenticationMethod() != Servatrice::AuthenticationSql) {
return false;
}
checkSql();
// Only migrate accounts that still use the legacy format; the query is a no-op otherwise.
QSqlQuery *query = prepareQuery(
"update {prefix}_users set password_sha512 = :verifier where name = :user and password_sha512 not like '$%'");
query->bindValue(":verifier", passwordVerifier);
query->bindValue(":user", user);
if (!execSqlQuery(query)) {
qCWarning(DatabaseInterfaceLog) << "Failed to submit password verifier for user" << user << query->lastError();
return false;
}
return true;
}
int Servatrice_DatabaseInterface::getUserIdInDB(const QString &name)
{
if (server->getAuthenticationMethod() == Servatrice::AuthenticationSql) {