Messy WIP for agent extensions

Sources/Packages/Sources/SSHProtocolKit/OpenSSHPublicKeyWriter.swift

@@ -19,7 +19,7 @@ public struct OpenSSHPublicKeyWriter: Sendable {
             ("nistp" + String(describing: secret.keyType.size)).lengthAndData +
             secret.publicKey.lengthAndData
         case .mldsa:
-            // https://www.ietf.org/archive/id/draft-sfluhrer-ssh-mldsa-04.txt
+            // https://datatracker.ietf.org/doc/html/draft-sfluhrer-ssh-mldsa-05
             openSSHIdentifier(for: secret.keyType).lengthAndData +
             secret.publicKey.lengthAndData
         case .rsa:

Sources/Packages/Sources/SSHProtocolKit/OpenSSHReader.swift

@@ -39,6 +39,18 @@ public final class OpenSSHReader {
         return convertEndianness ? T(value.bigEndian) : T(value)
     }
 
+    public func readNextByteAsBool() throws(OpenSSHReaderError) -> Bool {
+        let size = MemoryLayout<Bool>.size
+        guard remaining.count >= size else { throw .beyondBounds }
+        let lengthRange = 0..<size
+        let lengthChunk = remaining[lengthRange]
+        remaining.removeSubrange(lengthRange)
+        if remaining.isEmpty {
+            done = true
+        }
+        return unsafe lengthChunk.bytes.unsafeLoad(as: Bool.self)
+    }
+
     public func readNextChunkAsString(convertEndianness: Bool = true) throws(OpenSSHReaderError) -> String {
         try String(decoding: readNextChunk(convertEndianness: convertEndianness), as: UTF8.self)
     }

Sources/Packages/Sources/SSHProtocolKit/OpenSSHSignatureWriter.swift

@@ -17,7 +17,7 @@ public struct OpenSSHSignatureWriter: Sendable {
             // https://datatracker.ietf.org/doc/html/rfc5656#section-3.1
             ecdsaSignature(signature, keyType: secret.keyType)
         case .mldsa:
-            // https://datatracker.ietf.org/doc/html/draft-sfluhrer-ssh-mldsa-00#name-public-key-algorithms
+            // https://datatracker.ietf.org/doc/html/draft-sfluhrer-ssh-mldsa-05
             mldsaSignature(signature, keyType: secret.keyType)
         case .rsa:
             // https://datatracker.ietf.org/doc/html/rfc4253#section-6.6

Sources/Packages/Sources/SSHProtocolKit/SSHAgentProtocol.swift

@@ -19,7 +19,7 @@ extension SSHAgent {
         case lock
         case unlock
         case addSmartcardKeyConstrained
-        case protocolExtension
+        case protocolExtension(ProtocolExtension)
         case unknown(UInt8)
 
         public var protocolID: UInt8 {
@@ -60,18 +60,82 @@ extension SSHAgent {
 
         public struct SignatureRequestContext: Sendable, Codable {
             public let keyBlob: Data
-            public let dataToSign: Data
+            public let dataToSign: SignaturePayload
 
-            public init(keyBlob: Data, dataToSign: Data) {
+            public init(keyBlob: Data, dataToSign: SignaturePayload) {
                 self.keyBlob = keyBlob
                 self.dataToSign = dataToSign
             }
 
             public static var empty: SignatureRequestContext {
-                SignatureRequestContext(keyBlob: Data(), dataToSign: Data())
+                SignatureRequestContext(keyBlob: Data(), dataToSign: SignaturePayload(raw: Data(), decoded: nil))
+            }
+
+            public struct SignaturePayload: Sendable, Codable {
+
+                public let raw: Data
+                public let decoded: DecodedPayload?
+
+                public init(
+                    raw: Data,
+                    decoded: DecodedPayload?
+                ) {
+                    self.raw = raw
+                    self.decoded = decoded
+                }
+
+                public enum DecodedPayload: Sendable, Codable {
+                    case sshConnection(SSHConnectionPayload)
+                    case sshSig(SSHSigPayload)
+
+                    public struct SSHConnectionPayload: Sendable, Codable {
+
+                        public let username: String
+                        public let hasSignature: Bool
+                        public let publicKeyAlgorithm: String
+                        public let publicKey: Data
+                        public let hostKey: Data
+
+                        public init(
+                            username: String,
+                            hasSignature: Bool,
+                            publicKeyAlgorithm: String,
+                            publicKey: Data,
+                            hostKey: Data
+                        ) {
+                            self.username = username
+                            self.hasSignature = hasSignature
+                            self.publicKeyAlgorithm = publicKeyAlgorithm
+                            self.publicKey = publicKey
+                            self.hostKey = hostKey
+                        }
+
+                    }
+
+                    public struct SSHSigPayload: Sendable, Codable {
+
+                        public let namespace: String
+                        public let hashAlgorithm: String
+                        public let hash: Data
+
+                        public init(
+                            namespace: String,
+                            hashAlgorithm: String,
+                            hash: Data,
+                        ) {
+                            self.namespace = namespace
+                            self.hashAlgorithm = hashAlgorithm
+                            self.hash = hash
+                        }
+
+                    }
+                    
+                }
+
             }
         }
 
+
     }
 
     /// The type of the SSH Agent Response, as described in https://datatracker.ietf.org/doc/html/draft-miller-ssh-agent#section-5.1
@@ -88,8 +152,8 @@ extension SSHAgent {
             switch self {
             case .agentFailure: "SSH_AGENT_FAILURE"
             case .agentSuccess: "SSH_AGENT_SUCCESS"
-            case .agentIdentitiesAnswer: "SSH_AGENT_IDENTITIES_ANSWER"
+            case .agentIdentitiesAnswer: "SSH2_AGENT_IDENTITIES_ANSWER"
-            case .agentSignResponse: "SSH_AGENT_SIGN_RESPONSE"
+            case .agentSignResponse: "SSH2_AGENT_SIGN_RESPONSE"
             case .agentExtensionFailure: "SSH_AGENT_EXTENSION_FAILURE"
             case .agentExtensionResponse: "SSH_AGENT_EXTENSION_RESPONSE"
             }

Sources/Packages/Sources/SSHProtocolKit/SSHProtocolExtensions.swift

@@ -0,0 +1,76 @@
+import Foundation
+
+// Extensions, as defined in https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.agent
+
+extension SSHAgent {
+
+    public enum ProtocolExtension: CustomDebugStringConvertible, Codable, Sendable {
+        case openSSH(OpenSSHExtension)
+        case unknown(String)
+
+        public var debugDescription: String {
+            switch self {
+            case let .openSSH(protocolExtension):
+                protocolExtension.debugDescription
+            case .unknown(let string):
+                "Unknown (\(string))"
+            }
+        }
+
+        public static var empty: ProtocolExtension {
+            .unknown("empty")
+        }
+
+        private struct ProtocolExtensionParsingError: Error {}
+
+    }
+
+}
+
+extension SSHAgent.ProtocolExtension {
+
+    public enum OpenSSHExtension: CustomDebugStringConvertible, Codable, Sendable {
+        case sessionBind(SessionBindContext)
+        case unknown(String)
+
+        public static var domain: String {
+            "openssh.com"
+        }
+
+        public var name: String {
+            switch self {
+            case .sessionBind:
+                "session-bind"
+            case .unknown(let name):
+                name
+            }
+        }
+
+        public var debugDescription: String {
+            "\(name)@\(OpenSSHExtension.domain)"
+        }
+    }
+
+}
+
+extension SSHAgent.ProtocolExtension.OpenSSHExtension {
+
+    public struct SessionBindContext: Codable, Sendable {
+
+        public let hostKey: Data
+        public let sessionID: Data
+        public let signature: Data
+        public let forwarding: Bool
+
+        public init(hostKey: Data, sessionID: Data, signature: Data, forwarding: Bool) {
+            self.hostKey = hostKey
+            self.sessionID = sessionID
+            self.signature = signature
+            self.forwarding = forwarding
+        }
+
+        public static let empty = SessionBindContext(hostKey: Data(), sessionID: Data(), signature: Data(), forwarding: false)
+
+    }
+
+}

Sources/Packages/Sources/SecretAgentKit/Agent.swift

@@ -33,6 +33,7 @@ public final class Agent: Sendable {
 extension Agent {
 
     public func handle(request: SSHAgent.Request, provenance: SigningRequestProvenance) async -> Data {
+        logger.debug("Agent received request of type \(request.debugDescription)")
         // Depending on the launch context (such as after macOS update), the agent may need to reload secrets before acting
         await reloadSecretsIfNeccessary()
         var response = Data()
@@ -44,8 +45,14 @@ extension Agent {
                 logger.debug("Agent returned \(SSHAgent.Response.agentIdentitiesAnswer.debugDescription)")
             case .signRequest(let context):
                 response.append(SSHAgent.Response.agentSignResponse.data)
-                response.append(try await sign(data: context.dataToSign, keyBlob: context.keyBlob, provenance: provenance))
+                response.append(try await sign(data: context.dataToSign.raw, keyBlob: context.keyBlob, provenance: provenance))
                 logger.debug("Agent returned \(SSHAgent.Response.agentSignResponse.debugDescription)")
+            case .protocolExtension(.openSSH(.sessionBind(let bind))):
+                response = SSHAgent.Response.agentSuccess.data
+                _ = bind
+                // FIXME: STORE BIND IN KEYCHAIN
+                // FIXME: CLEAR OUT BINDS BASED ON EXPIRATION?
+                logger.debug("Agent returned \(SSHAgent.Response.agentSuccess.debugDescription)")
             case .unknown(let value):
                 logger.error("Agent received unknown request of type \(value).")
                 throw UnhandledRequestError()

Sources/Packages/Sources/SecretAgentKit/SSHAgentInputParser.swift

@@ -3,6 +3,8 @@ import OSLog
 import SecretKit
 import SSHProtocolKit
 
+import CryptoKit
+
 public protocol SSHAgentInputParserProtocol {
 
     func parse(data: Data) async throws -> SSHAgent.Request
@@ -53,8 +55,10 @@ public struct SSHAgentInputParser: SSHAgentInputParserProtocol {
             return .unlock
         case SSHAgent.Request.addSmartcardKeyConstrained.protocolID:
             return .addSmartcardKeyConstrained
-        case SSHAgent.Request.protocolExtension.protocolID:
+        case SSHAgent.Request.protocolExtension(.empty).protocolID:
-            return .protocolExtension
+            return .protocolExtension(try protocolExtension(from: body))
+//        case SSHAgent.Request.constrainExtension(.empty).protocolID:
+//            return .constrainExtension(try constrainExtension(from: body))
         default:
             return .unknown(rawRequestInt)
         }
@@ -64,12 +68,126 @@ public struct SSHAgentInputParser: SSHAgentInputParserProtocol {
 
 extension SSHAgentInputParser {
 
+    private enum Constants {
+        static let userAuthMagic: UInt8 = 50 // SSH2_MSG_USERAUTH_REQUEST
+        static let sshSigMagic = Data("SSHSIG".utf8)
+    }
+
     func signatureRequestContext(from data: Data) throws(OpenSSHReaderError) -> SSHAgent.Request.SignatureRequestContext {
         let reader = OpenSSHReader(data: data)
         let rawKeyBlob = try reader.readNextChunk()
         let keyBlob = certificatePublicKeyBlob(from: rawKeyBlob) ?? rawKeyBlob
-        let dataToSign = try reader.readNextChunk()
+        let rawPayload = try reader.readNextChunk()
-        return SSHAgent.Request.SignatureRequestContext(keyBlob: keyBlob, dataToSign: dataToSign)
+        let payload: SSHAgent.Request.SignatureRequestContext.SignaturePayload
+        if rawPayload.count > 6 && rawPayload[0..<6] == Constants.sshSigMagic {
+            // https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.sshsig#L79
+            let payloadReader = OpenSSHReader(data: rawPayload[6...])
+            let namespace = try payloadReader.readNextChunkAsString()
+            _ = try payloadReader.readNextChunk() // reserved
+            let hashAlgorithm = try payloadReader.readNextChunkAsString()
+            let hash = try payloadReader.readNextChunk()
+            payload = .init(
+                raw: data,
+                decoded: .init(
+                    .sshSig(
+                        .init(
+                            namespace: namespace,
+                            hashAlgorithm: hashAlgorithm,
+                            hash: hash
+                        )
+                    )
+                )
+            )
+        } else {
+            let payloadReader = OpenSSHReader(data: rawPayload)
+            do {
+                _ = try payloadReader.readNextChunk()
+                let magic = try payloadReader.readNextBytes(as: UInt8.self, convertEndianness: false)
+                if magic == Constants.userAuthMagic {
+                    let username = try payloadReader.readNextChunkAsString()
+                    _ = try payloadReader.readNextChunkAsString() // "ssh-connection"
+                    _ = try payloadReader.readNextChunkAsString() // "publickey-hostbound-v00@openssh.com"
+                    let hasSignature = try payloadReader.readNextByteAsBool()
+                    let pkAlg = try payloadReader.readNextChunkAsString()
+                    let pk = try payloadReader.readNextChunk()
+                    let hostKey = try payloadReader.readNextChunk()
+                    payload = .init(
+                        raw: rawPayload,
+                        decoded: .init(
+                            .sshConnection(
+                                .init(
+                                    username: username,
+                                    hasSignature: hasSignature,
+                                    publicKeyAlgorithm: pkAlg,
+                                    publicKey: pk,
+                                    hostKey: hostKey
+                                )
+                            )
+                        )
+                    )
+                } else {
+                    throw AgentParsingError.unknownRequest
+                }
+            } catch {
+                payload = .init(raw: rawPayload, decoded: nil)
+            }
+        }
+        return SSHAgent.Request.SignatureRequestContext(keyBlob: keyBlob, dataToSign: payload)
+    }
+
+    func protocolExtension(from data: Data) throws(AgentParsingError) -> SSHAgent.ProtocolExtension {
+        do {
+            let reader = OpenSSHReader(data: data)
+            let nameRaw = try reader.readNextChunkAsString()
+            let nameSplit = nameRaw.split(separator: "@")
+            guard nameSplit.count == 2 else {
+                throw AgentParsingError.invalidData
+            }
+            let (name, domain) = (nameSplit[0], nameSplit[1])
+            switch domain {
+            case SSHAgent.ProtocolExtension.OpenSSHExtension.domain:
+                switch name {
+                case SSHAgent.ProtocolExtension.OpenSSHExtension.sessionBind(.empty).name:
+                    let hostkeyBlob = try reader.readNextChunkAsSubReader()
+                    let hostKeyType = try hostkeyBlob.readNextChunkAsString()
+                    let hostKeyData = try hostkeyBlob.readNextChunk()
+                    let sessionID = try reader.readNextChunk()
+                    let signatureBlob = try reader.readNextChunkAsSubReader()
+                    _ = try signatureBlob.readNextChunk() // key type again
+                    let signature = try signatureBlob.readNextChunk()
+                    let forwarding = try reader.readNextByteAsBool()
+                    switch hostKeyType {
+                        // FIXME: FACTOR OUT?
+                        // FIXME: HANDLE OTHER KEYS
+                    case "ssh-ed25519":
+                        let hostKey = try CryptoKit.Curve25519.Signing.PublicKey(rawRepresentation: hostKeyData)
+                        guard hostKey.isValidSignature(signature, for: sessionID) else {
+                            throw AgentParsingError.invalidData
+                        }
+                    default:
+                        throw AgentParsingError.unhandledRequest
+                    }
+                    let context = SSHAgent.ProtocolExtension.OpenSSHExtension.SessionBindContext(
+                        hostKey: hostKeyData,
+                        sessionID: sessionID,
+                        signature: signature,
+                        forwarding: forwarding
+                    )
+                    return .openSSH(.sessionBind(context))
+                default:
+                    return .openSSH(.unknown(String(name)))
+                }
+            default:
+                return .unknown(nameRaw)
+            }
+
+        } catch let error as OpenSSHReaderError {
+            throw .openSSHReader(error)
+        } catch let error as AgentParsingError {
+            throw error
+        } catch {
+            throw .unknownRequest
+        }
     }
 
     func certificatePublicKeyBlob(from hash: Data) -> Data? {