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Merged
kruton merged 3 commits into from
May 7, 2026
Merged

More testing #137

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f544794
chore: add equalsverifier in other places
kruton May 4, 2026
8ff0d51
chore(AgentProtocol): make Agent more testable
kruton May 7, 2026
6ab3cdf
Potential fix for pull request finding
kruton May 7, 2026
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198 changes: 92 additions & 106 deletions sshlib/src/main/kotlin/org/connectbot/sshlib/client/AgentProtocolHandler.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,96 @@ internal fun interface SessionBindVerifier {
fun verify(hostKeyBlob: ByteArray, signature: ByteArray, data: ByteArray): Boolean
}

internal data class BindingEntry(val hostKeyBlob: ByteArray, val sessionId: ByteArray) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (javaClass != other?.javaClass) return false
other as BindingEntry
if (!hostKeyBlob.contentEquals(other.hostKeyBlob)) return false
if (!sessionId.contentEquals(other.sessionId)) return false
return true
}

override fun hashCode(): Int {
var result = hostKeyBlob.contentHashCode()
result = 31 * result + sessionId.contentHashCode()
return result
}
}

internal data class SignedDataComponents(
val methodName: String,
val destUsername: String,
val serverHostKeyBlob: ByteArray?,
) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (javaClass != other?.javaClass) return false
other as SignedDataComponents
if (methodName != other.methodName) return false
if (destUsername != other.destUsername) return false
if (!(serverHostKeyBlob == null && other.serverHostKeyBlob == null) &&
(
serverHostKeyBlob == null || other.serverHostKeyBlob == null ||
!serverHostKeyBlob.contentEquals(other.serverHostKeyBlob)
)
) {
return false
}
return true
}

override fun hashCode(): Int {
var result = methodName.hashCode()
result = 31 * result + destUsername.hashCode()
result = 31 * result + (serverHostKeyBlob?.contentHashCode() ?: 0)
return result
}
}

internal fun buildAgentMessage(messageType: Int, payload: ByteArray): ByteArray {
val totalLength = 1L + payload.size
val stream = ByteBufferKaitaiStream(4 + totalLength)
stream.writeU4be(totalLength)
stream.writeU1(messageType)
stream.writeBytes(payload)
stream.seek(0)
return stream.readBytesFull()
}

internal fun isConstraintSatisfied(
constraints: List<DestinationConstraint>,
components: SignedDataComponents,
bindingList: List<BindingEntry>,
): Boolean {
val isForwarding = bindingList.isNotEmpty()
val forwardingHopKey = if (bindingList.size >= 2) {
bindingList[bindingList.size - 2].hostKeyBlob
} else if (bindingList.size == 1) {
bindingList[0].hostKeyBlob
} else {
null
}

return constraints.any { c ->
val fromMatches = if (!isForwarding) {
c.fromHostname.isEmpty() && c.fromKeyspecs.isEmpty()
} else {
forwardingHopKey != null && c.fromKeyspecs.any { spec ->
spec.keyBlob.contentEquals(forwardingHopKey)
}
}
if (!fromMatches) return@any false

val usernameMatches = c.toUsername.isEmpty() || c.toUsername == components.destUsername
if (!usernameMatches) return@any false

val hostKeyMatches = components.serverHostKeyBlob != null &&
c.toHostspecs.any { spec -> spec.keyBlob.contentEquals(components.serverHostKeyBlob) }
hostKeyMatches
}
}

internal class AgentProtocolHandler(
private val provider: AgentProvider,
private val sessionInfo: AgentSessionInfo,
Expand All @@ -57,27 +147,9 @@ internal class AgentProtocolHandler(
const val SSH_AGENTC_EXTENSION: Int = 27
const val SSH_AGENT_SUCCESS: Int = 6

private const val METHOD_PUBLICKEY = "publickey"
private const val METHOD_PUBLICKEY_HOSTBOUND = "publickey-hostbound-v00@openssh.com"
}

private data class BindingEntry(val hostKeyBlob: ByteArray, val sessionId: ByteArray) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (javaClass != other?.javaClass) return false
other as BindingEntry
if (!hostKeyBlob.contentEquals(other.hostKeyBlob)) return false
if (!sessionId.contentEquals(other.sessionId)) return false
return true
}

override fun hashCode(): Int {
var result = hostKeyBlob.contentHashCode()
result = 31 * result + sessionId.contentHashCode()
return result
}
}

private val bindingList: MutableList<BindingEntry> = mutableListOf()

suspend fun handleRequest(requestBytes: ByteArray): ByteArray {
Expand Down Expand Up @@ -166,13 +238,11 @@ internal class AgentProtocolHandler(
return createFailureResponse()
}

// For direct connections with standard publickey auth (no embedded server host key),
// use the session's server host key as the implicit destination.
if (bindingList.isEmpty() && components.serverHostKeyBlob == null) {
components = components.copy(serverHostKeyBlob = sessionInfo.serverHostKey)
}

if (!isConstraintSatisfied(constraints, components)) {
if (!isConstraintSatisfied(constraints, components, bindingList)) {
logger.warn("Destination constraint not satisfied for key")
return createFailureResponse()
}
Expand Down Expand Up @@ -206,37 +276,6 @@ internal class AgentProtocolHandler(
}
}

private data class SignedDataComponents(
val methodName: String,
val destUsername: String,
val serverHostKeyBlob: ByteArray?,
) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (javaClass != other?.javaClass) return false
other as SignedDataComponents
if (methodName != other.methodName) return false
if (destUsername != other.destUsername) return false
if (!serverHostKeyBlob.contentEquals(other.serverHostKeyBlob)) return false
return true
}

override fun hashCode(): Int {
var result = methodName.hashCode()
result = 31 * result + destUsername.hashCode()
result = 31 * result + serverHostKeyBlob.contentHashCode()
return result
}
}

private fun ByteArray?.contentEquals(other: ByteArray?): Boolean {
if (this == null && other == null) return true
if (this == null || other == null) return false
return java.util.Arrays.equals(this, other)
}

private fun ByteArray?.contentHashCode(): Int = this?.contentHashCode() ?: 0

private fun parseSignedDataComponents(data: ByteArray): SignedDataComponents? = try {
val stream = ByteBufferKaitaiStream(data)
val sigData = UserauthPublickeySignatureDataAny(stream)
Expand All @@ -252,40 +291,6 @@ internal class AgentProtocolHandler(
null
}

private fun isConstraintSatisfied(
constraints: List<DestinationConstraint>,
components: SignedDataComponents,
): Boolean {
val isForwarding = bindingList.isNotEmpty()
// The forwarding hop key is the second-to-last binding (the host that relayed to us).
// The last binding is the destination's connection key, also represented in components.serverHostKeyBlob.
val forwardingHopKey = if (bindingList.size >= 2) {
bindingList[bindingList.size - 2].hostKeyBlob
} else if (bindingList.size == 1) {
bindingList[0].hostKeyBlob
} else {
null
}

return constraints.any { c ->
val fromMatches = if (!isForwarding) {
c.fromHostname.isEmpty() && c.fromKeyspecs.isEmpty()
} else {
forwardingHopKey != null && c.fromKeyspecs.any { spec ->
spec.keyBlob.contentEquals(forwardingHopKey)
}
}
if (!fromMatches) return@any false

val usernameMatches = c.toUsername.isEmpty() || c.toUsername == components.destUsername
if (!usernameMatches) return@any false

val hostKeyMatches = components.serverHostKeyBlob != null &&
c.toHostspecs.any { spec -> spec.keyBlob.contentEquals(components.serverHostKeyBlob) }
hostKeyMatches
}
}

private suspend fun handleExtension(message: SshAgentMessage): ByteArray {
logger.debug("Handling EXTENSION")

Expand All @@ -311,21 +316,18 @@ internal class AgentProtocolHandler(

val hostKeyBlob = bind.hostkey().data()
val sessionId = bind.sessionIdentifier().data()
val isForwarding = bind.isForwarding().toInt() != 0
val isForwarding = bind.isForwarding() != 0

// Replay protection: reject duplicate session IDs
if (bindingList.any { it.sessionId.contentEquals(sessionId) }) {
logger.warn("Session bind replay: session ID already recorded")
return createFailureResponse()
}

// For non-forwarding (origin) binds, verify the hostkey matches the connection's server key
if (!isForwarding && !hostKeyBlob.contentEquals(sessionInfo.serverHostKey)) {
logger.error("Session bind hostkey mismatch for non-forwarding bind")
return createFailureResponse()
}

// Cryptographically verify the session bind signature
if (!bindVerifier.verify(hostKeyBlob, bind.signature().data(), sessionId)) {
logger.error("Session bind signature verification failed")
return createFailureResponse()
Expand All @@ -343,22 +345,6 @@ internal class AgentProtocolHandler(
return payload
}

private fun buildAgentMessage(messageType: Int, payload: ByteArray): ByteArray {
val totalLength = 1 + payload.size
val buffer = ByteArray(4 + totalLength)

buffer[0] = ((totalLength shr 24) and 0xFF).toByte()
buffer[1] = ((totalLength shr 16) and 0xFF).toByte()
buffer[2] = ((totalLength shr 8) and 0xFF).toByte()
buffer[3] = (totalLength and 0xFF).toByte()

buffer[4] = messageType.toByte()

System.arraycopy(payload, 0, buffer, 5, payload.size)

return buffer
}

private fun createFailureResponse(): ByteArray = buildAgentMessage(SSH_AGENT_FAILURE, ByteArray(0))

private fun createSuccessResponse(): ByteArray = buildAgentMessage(SSH_AGENT_SUCCESS, ByteArray(0))
Expand Down
18 changes: 8 additions & 10 deletions sshlib/src/main/kotlin/org/connectbot/sshlib/client/SshConnection.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -706,16 +706,6 @@ class SshConnection(
return data.toByteArray()
}

private fun keyBlobAlgorithmName(publicKeyBlob: ByteArray): String? {
if (publicKeyBlob.size < 4) return null
val len = ((publicKeyBlob[0].toInt() and 0xFF) shl 24) or
((publicKeyBlob[1].toInt() and 0xFF) shl 16) or
((publicKeyBlob[2].toInt() and 0xFF) shl 8) or
(publicKeyBlob[3].toInt() and 0xFF)
if (len <= 0 || len > publicKeyBlob.size - 4) return null
return String(publicKeyBlob, 4, len, Charsets.US_ASCII)
}

private fun negotiateRsaAlgorithm(): String = SignatureEntry.negotiateRsaAlgorithm(serverSigAlgs)

/**
Expand Down Expand Up @@ -2773,3 +2763,11 @@ internal fun selectPasswordMethods(
else -> emptyList()
}
}

internal fun keyBlobAlgorithmName(publicKeyBlob: ByteArray): String? {
if (publicKeyBlob.size < 4) return null
val stream = ByteBufferKaitaiStream(publicKeyBlob)
val len = stream.readU4be()
if (len <= 0 || len > publicKeyBlob.size - 4) return null
return String(stream.readBytes(len), Charsets.US_ASCII)
}
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