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Harden passcode hashing with PBKDF2 #25

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Harden passcode hashing with PBKDF2 #25

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33 changes: 29 additions & 4 deletions src/kotlin/helpers/security/SecretHash.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -6,11 +6,24 @@ import androidx.core.content.edit
import org.telegram.messenger.FileLog
import org.telegram.messenger.Utilities
import java.nio.charset.StandardCharsets
import java.security.MessageDigest
import javax.crypto.SecretKeyFactory
import javax.crypto.spec.PBEKeySpec

// Salted SHA-256 for fork-local secrets (account passcodes, hidden-chats exit code).
// Salted PBKDF2-HMAC-SHA256 for fork-local secrets (account passcodes, hidden-chats exit code).
// Kept out of InuConfig/backups by design — callers store into their own prefs file.
object SecretHash {
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private fun hash(code: String, salt: ByteArray): String {
private const val PREFIX = "pbkdf2$"
private const val ITERATIONS = 120_000
private const val KEY_BITS = 256

private fun pbkdf2(code: String, salt: ByteArray, iterations: Int): String {
val spec = PBEKeySpec(code.toCharArray(), salt, iterations, KEY_BITS)
val dk = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256").generateSecret(spec).encoded
return PREFIX + iterations + "$" + Utilities.bytesToHex(dk)
}

private fun legacySha256(code: String, salt: ByteArray): String {
val pwd = code.toByteArray(StandardCharsets.UTF_8)
val bytes = ByteArray(32 + pwd.size)
System.arraycopy(salt, 0, bytes, 0, 16)
Expand All @@ -19,11 +32,14 @@ object SecretHash {
return Utilities.bytesToHex(Utilities.computeSHA256(bytes, 0, bytes.size.toLong()))
}

private fun constEq(a: String, b: String): Boolean =
MessageDigest.isEqual(a.toByteArray(StandardCharsets.UTF_8), b.toByteArray(StandardCharsets.UTF_8))

fun store(prefs: SharedPreferences, hashKey: String, saltKey: String, code: String) {
try {
val salt = ByteArray(16).also { Utilities.random.nextBytes(it) }
prefs.edit {
putString(hashKey, hash(code, salt))
putString(hashKey, pbkdf2(code, salt, ITERATIONS))
putString(saltKey, Base64.encodeToString(salt, Base64.DEFAULT))
}
} catch (e: Exception) {
Expand All @@ -38,7 +54,16 @@ object SecretHash {
} else {
val saltB64 = prefs.getString(saltKey, "") ?: ""
val salt = if (saltB64.isNotEmpty()) Base64.decode(saltB64, Base64.DEFAULT) else ByteArray(0)
stored == hash(code, salt)
if (stored.startsWith(PREFIX)) {
val sep = stored.indexOf('$', PREFIX.length)
val iterations = stored.substring(PREFIX.length, sep).toInt()
constEq(stored, pbkdf2(code, salt, iterations))
} else if (constEq(stored, legacySha256(code, salt))) {
store(prefs, hashKey, saltKey, code)
true
} else {
false
}
}
} catch (e: Exception) {
FileLog.e(e); false
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