chore: destroy sensitive data after use

[kruton]

Try to call .destroy() on items that can be destroyed. Implement Destroyable on classes where it makes sense. Add a .zeroize() function for the Keys class to aid in sensitive value wiping.

[Copilot]

Pull request overview

This PR aims to reduce lifetime of sensitive cryptographic material by adding explicit destruction/zeroization hooks across the SSH transport and crypto layers, and invoking them after key exchange / rekey operations.

Changes:

• Add Destroyable support to packet crypto interfaces and implement destroy() in several KEX/cipher/MAC classes.
• Zeroize derived key material via a new KeyDerivation.Keys.zeroize() and wipe KEX-related buffers after NEWKEYS.
• Proactively destroy/replace active crypto instances when enabling new encryption modes.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
sshlib/src/main/kotlin/org/connectbot/sshlib/transport/PacketIO.kt	Destroys previous cipher/MAC/AEAD instances when reconfiguring encryption.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketMac.kt	Makes PacketMac Destroyable with default methods.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketCipher.kt	Makes PacketCipher Destroyable with default methods.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketAead.kt	Makes PacketAead Destroyable with default methods.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/MlKemHybridKeyExchange.kt	Adds destroy() to wipe ML-KEM and X25519 private keys.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/KeyDerivation.kt	Adds Keys.zeroize() and wipes intermediate digest buffers in derivation.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/KexAlgorithm.kt	Makes KEX algorithms Destroyable.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha512.kt	Attempts to add destroy logic for MAC key material.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha256.kt	Attempts to add destroy logic for MAC key material.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha1.kt	Attempts to add destroy logic for MAC key material.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/EcdhKeyExchange.kt	Adds destroy() to destroy underlying private key if supported.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/DiffieHellmanGroupExchange.kt	Clears DH private parameters after shared secret computation and on destroy.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/DiffieHellman.kt	Clears DH private key after shared secret computation and on destroy.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/Curve25519KeyExchange.kt	Avoids !! and adds destroy() to zeroize X25519 private key bytes.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/ChaCha20Poly1305Cipher.kt	Attempts to add destroy logic for AEAD key material.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/AesGcmCipher.kt	Attempts to add destroy logic for AEAD key material.
sshlib/src/main/kotlin/org/connectbot/sshlib/client/SshConnection.kt	Copies sessionId, wipes KEX buffers, destroys KEX object, and zeroizes derived keys.

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[Copilot]

Pull request overview

This PR strengthens in-memory hygiene across the SSH crypto/transport stack by explicitly destroying/zeroizing key material and crypto primitives after they’re no longer needed (especially across re-key), reducing the lifetime of sensitive data in RAM.

Changes:

• Add Destroyable support and call .destroy() when swapping packet encryption/MAC/AEAD state.
• Add key material wiping (zeroize() / fill(0)) for derived keys, KEX ephemeral secrets, and connection transcript buffers.
• Ensure session ID and KEX-related buffers are copied and later wiped without affecting shared references.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
sshlib/src/main/kotlin/org/connectbot/sshlib/transport/PacketIO.kt	Destroys previous cipher/MAC/AEAD instances when enabling new encryption modes.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketMac.kt	Makes packet MACs Destroyable (with default implementations).
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketCipher.kt	Makes packet ciphers Destroyable (with default implementations).
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/PacketAead.kt	Makes AEAD ciphers Destroyable (with default implementations).
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/MlKemHybridKeyExchange.kt	Adds destroy() to wipe ML-KEM + X25519 private key buffers.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/KeyDerivation.kt	Adds Keys.zeroize() and wipes intermediate digest material during derivation.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/KexAlgorithm.kt	Extends Destroyable so KEX implementations can be destroyed after NEWKEYS.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha512.kt	Adds destroy() calling SecretKeySpec.destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha256.kt	Adds destroy() calling SecretKeySpec.destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/HmacSha1.kt	Adds destroy() calling SecretKeySpec.destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/EcdhKeyExchange.kt	Adds destroy() to drop and destroy the client private key if supported.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/DiffieHellmanGroupExchange.kt	Drops DH-GEX private/group params after use; adds destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/DiffieHellman.kt	Drops DH private key after computing shared secret; adds destroy().
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/Curve25519KeyExchange.kt	Avoids !! and adds destroy() to wipe the X25519 private key bytes.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/ChaCha20Poly1305Cipher.kt	Adds destroy() to destroy key specs.
sshlib/src/main/kotlin/org/connectbot/sshlib/crypto/AesGcmCipher.kt	Adds destroy() to destroy key spec.
sshlib/src/main/kotlin/org/connectbot/sshlib/client/SshConnection.kt	Copies/wipes session/KEX buffers; destroys KEX and wipes shared secret/exchange hash; zeroizes derived keys after installing ciphers.

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