Restrict agent signing path

[kruton]

No description provided.

[Copilot]

Pull request overview

Adds support for OpenSSH agent destination constraints / host-bound publickey auth and strengthens key-material lifecycle management to better restrict where agent signatures can be used.

Changes:

• Add parsing/handling for SSH_MSG_EXT_INFO (server-sig-algs, publickey-hostbound@openssh.com) and negotiate RSA signature algorithm accordingly.
• Implement agent-side destination constraint enforcement and session-bind verification plumbing, with new unit/integration tests.
• Add zeroization/destroy hooks across KEX + packet crypto and wipe transient key material after use.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sshlib/src/test/resources/openssh-server/Dockerfile	Expands OpenSSH test server config to permit ssh-rsa pubkeys for compatibility testing.
sshlib/src/test/kotlin/org/connectbot/sshlib/crypto/AlgorithmsTest.kt	Adds unit tests for RSA signature algorithm negotiation.
sshlib/src/test/kotlin/org/connectbot/sshlib/client/SshClientIntegrationTest.kt	Adds integration coverage for ssh-rsa-only servers and default rsa-sha2 negotiation.
sshlib/src/test/kotlin/org/connectbot/sshlib/HostBoundSignatureDataTest.kt	Adds tests for host-bound signature-data encoding/parsing.
sshlib/src/test/kotlin/org/connectbot/sshlib/ExtInfoProcessingTest.kt	Adds tests for EXT_INFO parsing of host-bound + server-sig-algs.
sshlib/src/test/kotlin/org/connectbot/sshlib/AgentProtocolTest.kt	Updates agent protocol tests to cover bind verification + forwarding bind behavior.
sshlib/src/test/kotlin/org/connectbot/sshlib/AgentDestinationConstraintTest.kt	Adds tests for restrict-destination constraint enforcement and identity visibility.
sshlib/src/main/kotlin/org/connectbot/sshlib/transport/PacketIO.kt	Destroys old cipher/MAC/AEAD instances when switching encryption modes.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/RsaSignatureAlgorithm.kt	Correctly maps ssh-rsa to SHA1withRSA and centralizes mapping logic.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketMac.kt	Makes MACs destroyable for key zeroization.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketCipher.kt	Makes ciphers destroyable for key zeroization.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketAead.kt	Makes AEADs destroyable for key zeroization.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/MlKemHybridKeyExchange.kt	Adds private key zeroization.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/KeyDerivation.kt	Adds key/IV zeroization and clears intermediate digest material.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/KexAlgorithm.kt	Adds zeroize() contract for KEX implementations.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha512.kt	Zeroizes MAC key on destroy.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha256.kt	Zeroizes MAC key on destroy.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha1.kt	Zeroizes MAC key on destroy.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/EcdhKeyExchange.kt	Destroys private key material after KEX.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/DiffieHellmanGroupExchange.kt	Clears DH-GEX private parameters and adds zeroize().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/DiffieHellman.kt	Clears DH private key and adds zeroize().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/Curve25519KeyExchange.kt	Adds private key zeroization.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/ChaCha20Poly1305Cipher.kt	Stores key for destroy-time wiping and implements destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/Algorithms.kt	Adds ext-info-c to default KEX list and RSA signature negotiation helper.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/AesGcmCipher.kt	Stores key material for destroy-time wiping and implements destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/client/SshConnection.kt	Adds EXT_INFO parsing, host-bound auth request support, RSA algorithm negotiation, and post-KEX zeroization.
sshlib/src/main/kotlin/org/connectbot/sshlib/client/AgentProtocolHandler.kt	Implements destination constraint filtering/enforcement and session-bind verification hooks.
sshlib/src/main/kotlin/org/connectbot/sshlib/AgentProvider.kt	Extends agent identity API to carry destination constraints and adds constraint model types.
sshlib/api.txt	Updates public API surface for new AgentIdentity parameter + new model types.
protocol/src/main/resources/kaitai/userauth_request_publickey_hostbound.ksy	Adds Kaitai schema for host-bound publickey auth request fields.
protocol/src/main/resources/kaitai/userauth_publickey_signature_data_any.ksy	Adds Kaitai schema to parse both standard and host-bound signature data.
protocol/src/main/resources/kaitai/userauth_publickey_hostbound_signature_data.ksy	Adds Kaitai schema for host-bound signature data construction/parsing.
protocol/src/main/resources/kaitai/ssh_msg_userauth_request.ksy	Adds method switch case for host-bound publickey auth.
protocol/src/main/resources/kaitai/restrict_destination_constraint.ksy	Adds Kaitai schema for restrict-destination agent key constraints.
.gitignore	Ignores .worktrees/.

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[Copilot]

Unused import: createAsciiString is imported but never used. This will fail ktlint/spotless checks (no-unused-imports). Remove the unused import.

Suggested change

import org.connectbot.sshlib.protocol.createAsciiString