58 lines
2.0 KiB
Swift
58 lines
2.0 KiB
Swift
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import Foundation
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import CryptoKit
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/// End-to-end encryption for revealed conversations.
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///
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/// Uses X25519 key agreement + ChaChaPoly AEAD, the same primitives family
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/// used by Signal. The server only ever sees ciphertext and opaque key IDs —
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/// it cannot read message contents.
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struct CryptoManager {
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// MARK: - Key pair
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func generateKeyPair() -> (privateKey: Curve25519.KeyAgreement.PrivateKey,
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publicKey: Curve25519.KeyAgreement.PublicKey) {
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let privateKey = Curve25519.KeyAgreement.PrivateKey()
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return (privateKey, privateKey.publicKey)
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}
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// MARK: - Session establishment
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/// Derive a shared symmetric session key from two key pairs.
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func deriveSessionKey(
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myPrivate: Curve25519.KeyAgreement.PrivateKey,
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theirPublic: Curve25519.KeyAgreement.PublicKey
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) throws -> SymmetricKey {
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let shared = try myPrivate.sharedSecretFromKeyAgreement(with: theirPublic)
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// Salt with a fixed app domain string to keep keys per-app.
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return shared.hkdfDerivedSymmetricKey(
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using: SHA256.self,
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salt: Data("proximity.e2e.v1".utf8),
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sharedInfo: Data(),
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outputByteCount: 32
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)
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}
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// MARK: - Message encryption
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func encrypt(_ plaintext: Data, using key: SymmetricKey) throws -> Data {
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let sealed = try ChaChaPoly.seal(plaintext, using: key)
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return sealed.combined
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}
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func decrypt(_ combined: Data, using key: SymmetricKey) throws -> Data {
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let box = try ChaChaPoly.SealedBox(combined: combined)
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return try ChaChaPoly.open(box, using: key)
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}
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// MARK: - Signatures (for token authenticity)
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func sign(_ data: Data, with key: Curve25519.Signing.PrivateKey) throws -> Data {
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try key.signature(for: data)
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}
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func verify(_ data: Data, signature: Data, with key: Curve25519.Signing.PublicKey) -> Bool {
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key.isValidSignature(signature, for: data)
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}
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}
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