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31 lines
2.0 KiB
Swift
31 lines
2.0 KiB
Swift
import CryptoSwift
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import SessionUtilitiesKit
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import Sodium
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extension MessageReceiver {
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internal static func decryptWithSessionProtocol(ciphertext: Data, using x25519KeyPair: ECKeyPair) throws -> (plaintext: Data, senderX25519PublicKey: String) {
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let recipientX25519PrivateKey = x25519KeyPair.privateKey
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let recipientX25519PublicKey = Data(hex: x25519KeyPair.hexEncodedPublicKey.removing05PrefixIfNeeded())
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let sodium = Sodium()
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let signatureSize = sodium.sign.Bytes
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let ed25519PublicKeySize = sodium.sign.PublicKeyBytes
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// 1. ) Decrypt the message
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guard let plaintextWithMetadata = sodium.box.open(anonymousCipherText: Bytes(ciphertext), recipientPublicKey: Box.PublicKey(Bytes(recipientX25519PublicKey)),
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recipientSecretKey: Bytes(recipientX25519PrivateKey)), plaintextWithMetadata.count > (signatureSize + ed25519PublicKeySize) else { throw Error.decryptionFailed }
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// 2. ) Get the message parts
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let signature = Bytes(plaintextWithMetadata[plaintextWithMetadata.count - signatureSize ..< plaintextWithMetadata.count])
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let senderED25519PublicKey = Bytes(plaintextWithMetadata[plaintextWithMetadata.count - (signatureSize + ed25519PublicKeySize) ..< plaintextWithMetadata.count - signatureSize])
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let plaintext = Bytes(plaintextWithMetadata[0..<plaintextWithMetadata.count - (signatureSize + ed25519PublicKeySize)])
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// 3. ) Verify the signature
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let verificationData = plaintext + senderED25519PublicKey + recipientX25519PublicKey
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let isValid = sodium.sign.verify(message: verificationData, publicKey: senderED25519PublicKey, signature: signature)
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guard isValid else { throw Error.invalidSignature }
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// 4. ) Get the sender's X25519 public key
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guard let senderX25519PublicKey = sodium.sign.toX25519(ed25519PublicKey: senderED25519PublicKey) else { throw Error.decryptionFailed }
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return (Data(plaintext), "05" + senderX25519PublicKey.toHexString())
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}
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}
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