BITAU-98 Add EncryptionUtils helper functions to the bridge SDK

bridge/src/main/java/com/bitwarden/bridge/util/EncryptionUtils.kt

@@ -0,0 +1,76 @@
+package com.bitwarden.bridge.util
+
+import com.bitwarden.bridge.IBridgeService
+import com.bitwarden.bridge.model.EncryptedSharedAccountData
+import com.bitwarden.bridge.model.SharedAccountData
+import com.bitwarden.bridge.model.SymmetricEncryptionKeyData
+import com.bitwarden.bridge.model.toByteArrayContainer
+import kotlinx.serialization.encodeToString
+import java.security.MessageDigest
+import java.security.SecureRandom
+import javax.crypto.Cipher
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+import javax.crypto.spec.SecretKeySpec
+
+/**
+ * Generate a symmetric [SecretKey] that will used for encrypting IPC traffic.
+ *
+ * This is intended to be used for implementing [IBridgeService.getSymmetricEncryptionKeyData].
+ */
+fun generateSecretKey(): SecretKey {
+    val keygen = KeyGenerator.getInstance("AES")
+    keygen.init(256, SecureRandom())
+    return keygen.generateKey()
+}
+
+/**
+ * Generate a fingerprint for the given symmetric key.
+ *
+ * This is intended to be used for implementing
+ * [IBridgeService.checkSymmetricEncryptionKeyFingerprint], which allows callers of the service
+ * to verify that they have the correct symmetric key without actually having to send the key.
+ */
+fun SymmetricEncryptionKeyData.toFingerprint(): ByteArray {
+    val messageDigest = MessageDigest.getInstance("SHA-256")
+    messageDigest.reset()
+    messageDigest.update(this.symmetricEncryptionKey.byteArray)
+    return messageDigest.digest()
+}
+
+/**
+ * Encrypt [SharedAccountData].
+ *
+ * This is intended to be used by the main Bitwarden app during a [IBridgeService.syncAccounts] call.
+ *
+ * TODO: consider what error handling should be involved here.
+ */
+fun SharedAccountData.toEncryptedSharedAccountData(
+    symmetricEncryptionKeyData: SymmetricEncryptionKeyData,
+): EncryptedSharedAccountData {
+    val encodedKey = symmetricEncryptionKeyData.symmetricEncryptionKey.byteArray
+    val key = encodedKey.toSecretKey()
+    val cipher = generateCipher()
+    cipher.init(Cipher.ENCRYPT_MODE, key)
+    val jsonString = JSON.encodeToString(this)
+
+    val encryptedJsonString = cipher.doFinal(jsonString.encodeToByteArray()).toByteArrayContainer()
+    return EncryptedSharedAccountData(
+        initializationVector = cipher.iv.toByteArrayContainer(),
+        encryptedAccountsJson = encryptedJsonString,
+    )
+}
+
+/**
+ * Convert the given [ByteArray] to a [SecretKey].
+ */
+private fun ByteArray.toSecretKey(): SecretKey =
+    SecretKeySpec(this, 0, this.size, "AES")
+
+/**
+ * Helper function for generating a [Cipher] that can be used for encrypting/decrypting using
+ * [SymmetricEncryptionKeyData].
+ */
+private fun generateCipher(): Cipher =
+    Cipher.getInstance("AES/CBC/PKCS5PADDING")
+