Sketching out.

Sources/Packages/Package.swift

@@ -28,6 +28,9 @@ let package = Package(
         .library(
             name: "XPCWrappers",
             targets: ["XPCWrappers"]),
+        .library(
+            name: "SSHProtocolKit",
+            targets: ["SSHProtocolKit"]),
     ],
     dependencies: [
     ],
@@ -57,7 +60,7 @@ let package = Package(
         ),
         .target(
             name: "SecretAgentKit",
-            dependencies: ["SecretKit"],
+            dependencies: ["SecretKit", "SSHProtocolKit"],
             resources: [localization],
             swiftSettings: swiftSettings,
         ),
@@ -65,9 +68,19 @@ let package = Package(
             name: "SecretAgentKitTests",
             dependencies: ["SecretAgentKit"],
         ),
+        .target(
+            name: "SSHProtocolKit",
+            dependencies: ["SecretKit"],
+            resources: [localization],
+            swiftSettings: swiftSettings,
+        ),
+        .testTarget(
+            name: "SSHProtocolKitTests",
+            dependencies: ["SSHProtocolKit"],
+        ),
         .target(
             name: "Brief",
-            dependencies: ["XPCWrappers"],
+            dependencies: ["XPCWrappers", "SSHProtocolKit"],
             resources: [localization],
             swiftSettings: swiftSettings,
         ),

Sources/Packages/Sources/SSHProtocolKit/Data+Hex.swift

@@ -0,0 +1,37 @@
+import Foundation
+import CryptoKit
+
+public struct HexDataStyle<SequenceType: Sequence>: Hashable, Codable {
+
+    let separator: String
+
+    public init(separator: String) {
+        self.separator = separator
+    }
+
+}
+
+extension HexDataStyle: FormatStyle where SequenceType.Element == UInt8 {
+
+    public func format(_ value: SequenceType) -> String {
+        value
+            .compactMap { ("0" + String($0, radix: 16, uppercase: false)).suffix(2) }
+            .joined(separator: separator)
+    }
+
+}
+
+extension FormatStyle where Self == HexDataStyle<Data> {
+
+    public static func hex(separator: String = "") -> HexDataStyle<Data> {
+        HexDataStyle(separator: separator)
+    }
+
+}
+extension FormatStyle where Self == HexDataStyle<Insecure.MD5Digest> {
+
+    public static func hex(separator: String = ":") -> HexDataStyle<Insecure.MD5Digest> {
+        HexDataStyle(separator: separator)
+    }
+
+}

Sources/Packages/Sources/SSHProtocolKit/OpenSSHCertificate.swift

@@ -0,0 +1,65 @@
+import Foundation
+import OSLog
+
+public struct OpenSSHCertificate: Sendable, Codable, Equatable, Hashable, Identifiable, CustomDebugStringConvertible {
+
+    public var id: Int { hashValue }
+    public var type: CertificateType
+    public let name: String?
+    public let data: Data
+
+    public var debugDescription: String {
+        "OpenSSH Certificate \(name, default: "Unnamed"): \(data.formatted(.hex()))"
+    }
+
+}
+
+extension OpenSSHCertificate {
+
+    public enum CertificateType: String, Sendable, Codable {
+        case ecdsa256 = "ecdsa-sha2-nistp256-cert-v01@openssh.com"
+        case ecdsa384 = "ecdsa-sha2-nistp384-cert-v01@openssh.com"
+        case nistp521 = "ecdsa-sha2-nistp521-cert-v01@openssh.com"
+
+        var keyIdentifier: String {
+            rawValue.replacingOccurrences(of: "-cert-v01@openssh.com", with: "")
+        }
+    }
+
+}
+
+public protocol OpenSSHCertificateParserProtocol {
+    func parse(data: Data) async throws -> OpenSSHCertificate
+}
+
+public struct OpenSSHCertificateParser: OpenSSHCertificateParserProtocol, Sendable {
+
+    private let logger = Logger(subsystem: "com.maxgoedjen.secretive", category: "OpenSSHCertificateParser")
+
+    public init() {
+    }
+
+    public func parse(data: Data) throws(OpenSSHCertificateError) -> OpenSSHCertificate {
+        let string = String(decoding: data, as: UTF8.self)
+        var elements = string
+            .trimmingCharacters(in: .whitespacesAndNewlines)
+            .components(separatedBy: " ")
+        guard elements.count >= 2 else {
+            throw OpenSSHCertificateError.parsingFailed
+        }
+        let typeString = elements.removeFirst()
+        guard let type = OpenSSHCertificate.CertificateType(rawValue: typeString) else { throw .unsupportedType }
+        let encodedKey = elements.removeFirst()
+        guard let decoded = Data(base64Encoded: encodedKey)  else {
+            throw OpenSSHCertificateError.parsingFailed
+        }
+        let name = elements.first
+        return OpenSSHCertificate(type: type, name: name, data: decoded)
+    }
+
+}
+
+public enum OpenSSHCertificateError: Error, Codable {
+    case unsupportedType
+    case parsingFailed
+}

Sources/Packages/Sources/SSHProtocolKit/OpenSSHPublicKeyWriter.swift

@@ -1,5 +1,6 @@
 import Foundation
 import CryptoKit
+import SecretKit
 
 /// Generates OpenSSH representations of the public key sof secrets.
 public struct OpenSSHPublicKeyWriter: Sendable {
@@ -49,9 +50,7 @@ public struct OpenSSHPublicKeyWriter: Sendable {
     /// Generates an OpenSSH MD5 fingerprint string.
     /// - Returns: OpenSSH MD5 fingerprint string.
     public func openSSHMD5Fingerprint<SecretType: Secret>(secret: SecretType) -> String {
-        Insecure.MD5.hash(data: data(secret: secret))
-            .compactMap { ("0" + String($0, radix: 16, uppercase: false)).suffix(2) }
-            .joined(separator: ":")
+        Insecure.MD5.hash(data: data(secret: secret)).formatted(.hex(separator: ":"))
     }
 
     public func comment<SecretType: Secret>(secret: SecretType) -> String {

Sources/Packages/Sources/SSHProtocolKit/OpenSSHSignatureWriter.swift

@@ -1,5 +1,6 @@
 import Foundation
 import CryptoKit
+import SecretKit
 
 /// Generates OpenSSH representations of Secrets.
 public struct OpenSSHSignatureWriter: Sendable {

Sources/Packages/Sources/SSHProtocolKit/PublicKeyStandinFileController.swift

@@ -1,5 +1,6 @@
 import Foundation
 import OSLog
+import SecretKit
 
 /// Controller responsible for writing public keys to disk, so that they're easily accessible by scripts.
 public final class PublicKeyFileStoreController: Sendable {

Sources/Packages/Sources/SSHProtocolKit/SSHAgentInputParser.swift

@@ -74,21 +74,16 @@ extension SSHAgentInputParser {
     func certificatePublicKeyBlob(from hash: Data) -> Data? {
         let reader = OpenSSHReader(data: hash)
         do {
-            let certType = String(decoding: try reader.readNextChunk(), as: UTF8.self)
-            switch certType {
-            case "ecdsa-sha2-nistp256-cert-v01@openssh.com",
-                "ecdsa-sha2-nistp384-cert-v01@openssh.com",
-                "ecdsa-sha2-nistp521-cert-v01@openssh.com":
-                _ = try reader.readNextChunk() // nonce
-                let curveIdentifier = try reader.readNextChunk()
-                let publicKey = try reader.readNextChunk()
-                let openSSHIdentifier = certType.replacingOccurrences(of: "-cert-v01@openssh.com", with: "")
-                return openSSHIdentifier.lengthAndData +
-                curveIdentifier.lengthAndData +
+            let certType = try reader.readNextChunkAsString()
+            guard let certType = OpenSSHCertificate.CertificateType(rawValue: certType) else { return nil }
+            _ = try reader.readNextChunk() // nonce
+            let curveIdentifier = try reader.readNextChunk()
+            let publicKey = try reader.readNextChunk()
+            let openSSHIdentifier = certType.keyIdentifier
+            return openSSHIdentifier.lengthAndData +
+            curveIdentifier.lengthAndData +
                 publicKey.lengthAndData
-            default:
-                return nil
-            }
+            
         } catch {
             return nil
         }

Sources/Packages/Sources/SecretAgentKit/Agent.swift

@@ -3,6 +3,7 @@ import CryptoKit
 import OSLog
 import SecretKit
 import AppKit
+import SSHProtocolKit
 
 /// The `Agent` is an implementation of an SSH agent. It manages coordination and access between a socket, traces requests, notifies witnesses and passes requests to stores.
 public final class Agent: Sendable {
@@ -11,7 +12,7 @@ public final class Agent: Sendable {
     private let witness: SigningWitness?
     private let publicKeyWriter = OpenSSHPublicKeyWriter()
     private let signatureWriter = OpenSSHSignatureWriter()
-    private let certificateHandler = OpenSSHCertificateHandler()
+//    private let certificateHandler = OpenSSHCertificateHandler()
     private let logger = Logger(subsystem: "com.maxgoedjen.secretive.secretagent", category: "Agent")
 
     /// Initializes an agent with a store list and a witness.
@@ -23,7 +24,7 @@ public final class Agent: Sendable {
         self.storeList = storeList
         self.witness = witness
         Task { @MainActor in
-            await certificateHandler.reloadCertificates(for: storeList.allSecrets)
+//            await certificateHandler.reloadCertificates(for: storeList.allSecrets)
         }
     }
     
@@ -66,7 +67,7 @@ extension Agent {
     /// - Returns: An OpenSSH formatted Data payload listing the identities available for signing operations.
     func identities() async -> Data {
         let secrets = await storeList.allSecrets
-        await certificateHandler.reloadCertificates(for: secrets)
+//        await certificateHandler.reloadCertificates(for: secrets)
         var count = 0
         var keyData = Data()
 
@@ -75,12 +76,12 @@ extension Agent {
             keyData.append(keyBlob.lengthAndData)
             keyData.append(publicKeyWriter.comment(secret: secret).lengthAndData)
             count += 1
-
-            if let (certificateData, name) = try? await certificateHandler.keyBlobAndName(for: secret) {
-                keyData.append(certificateData.lengthAndData)
-                keyData.append(name.lengthAndData)
-                count += 1
-            }
+            
+//            if let (certificateData, name) = try? await certificateHandler.keyBlobAndName(for: secret) {
+//                keyData.append(certificateData.lengthAndData)
+//                keyData.append(name.lengthAndData)
+//                count += 1
+//            }
         }
         logger.log("Agent enumerated \(count) identities")
         var countBigEndian = UInt32(count).bigEndian
@@ -95,7 +96,7 @@ extension Agent {
     /// - Returns: An OpenSSH formatted Data payload containing the signed data response.
     func sign(data: Data, keyBlob: Data, provenance: SigningRequestProvenance) async throws -> Data {
         guard let (secret, store) = await secret(matching: keyBlob) else {
-            let keyBlobHex = keyBlob.compactMap { ("0" + String($0, radix: 16, uppercase: false)).suffix(2) }.joined()
+            let keyBlobHex = keyBlob.formatted(.hex())
             logger.debug("Agent did not have a key matching \(keyBlobHex)")
             throw NoMatchingKeyError()
         }

Sources/Packages/Sources/SecretAgentKit/OpenSSHCertificateHandler.swift

@@ -1,6 +1,7 @@
 import Foundation
 import OSLog
 import SecretKit
+import SSHProtocolKit
 
 /// Manages storage and lookup for OpenSSH certificates.
 public actor OpenSSHCertificateHandler: Sendable {
@@ -21,9 +22,6 @@ public actor OpenSSHCertificateHandler: Sendable {
             logger.log("No certificates, short circuiting")
             return
         }
-        keyBlobsAndNames = secrets.reduce(into: [:]) { partialResult, next in
-            partialResult[next] = try? loadKeyblobAndName(for: next)
-        }
     }
 
     /// Attempts to find an OpenSSH Certificate  that corresponds to a ``Secret``
@@ -32,57 +30,6 @@ public actor OpenSSHCertificateHandler: Sendable {
     public func keyBlobAndName<SecretType: Secret>(for secret: SecretType) throws -> (Data, Data)? {
         keyBlobsAndNames[AnySecret(secret)]
     }
-    
-    /// Attempts to find an OpenSSH Certificate  that corresponds to a ``Secret``
-    /// - Parameter secret: The secret to search for a certificate with
-    /// - Returns: A (``Data``, ``Data``) tuple containing the certificate and certificate name, respectively.
-    private func loadKeyblobAndName<SecretType: Secret>(for secret: SecretType) throws -> (Data, Data)? {
-        let certificatePath = publicKeyFileStoreController.sshCertificatePath(for: secret)
-        guard FileManager.default.fileExists(atPath: certificatePath) else {
-            return nil
-        }
-
-        logger.debug("Found certificate for \(secret.name)")
-        let certContent = try String(contentsOfFile:certificatePath, encoding: .utf8)
-        let certElements = certContent.trimmingCharacters(in: .whitespacesAndNewlines).components(separatedBy: " ")
-
-        guard certElements.count >= 2 else {
-            logger.warning("Certificate found for \(secret.name) but failed to load")
-            throw OpenSSHCertificateError.parsingFailed
-        }
-        guard let certDecoded = Data(base64Encoded: certElements[1] as String)  else {
-            logger.warning("Certificate found for \(secret.name) but failed to decode base64 key")
-            throw OpenSSHCertificateError.parsingFailed
-        }
-
-        if certElements.count >= 3 {
-            let certName = Data(certElements[2].utf8)
-            return (certDecoded, certName)
-        }
-        let certName = Data(secret.name.utf8)
-        logger.info("Certificate for \(secret.name) does not have a name tag, using secret name instead")
-        return (certDecoded, certName)
-    }
 
 }
 
-extension OpenSSHCertificateHandler {
-
-    enum OpenSSHCertificateError: LocalizedError {
-        case unsupportedType
-        case parsingFailed
-        case doesNotExist
-
-        public var errorDescription: String? {
-            switch self {
-            case .unsupportedType:
-                return "The key type was unsupported"
-            case .parsingFailed:
-                return "Failed to properly parse the SSH certificate"
-            case .doesNotExist:
-                return "Certificate does not exist"
-            }
-        }
-    }
-
-}