modules/crypto.js

// ============================================================================
// File: modules/crypto.js
// ============================================================================

(function(global) {
    'use strict';

    const CURRENT_CRYPTO_VERSION = "3.0.0-AES-256-GCM-SHA-256-Strict-WebCrypto-RTL";
    const SECURE_HEADER_V3 = "FTE_SECURE_PACKET_SHA256_V3:";
    const TOKEN_HEADER = "FTE_TOKEN_SHA256_V3:";
    const BACKUP_HEADER = "";
    
    // Constant security salting bound to SHA-256 algorithm
    const HASH_KEY_SALT = "FritreeKeySalt_2026_StrictSHA256_MaximumHardenSalt_EnterpriseForce";
    const DERIVATION_SALT = "FritreeDerivationSalt_2026_StrictSHA256_SolidStateSymmetricSalt";
    const PBKDF2_ITERATIONS = 120000; 

    let cachedMasterKey = null;
    const derivedKeyCache = new Map();
    const derivedHmacKeyCache = new Map();

    /**
     * Clears sensitive arrays from memory when no longer required
     * @param {ArrayBuffer|TypedArray} buffer - Target memory buffer
     */
    function secureWipe(buffer) {
        if (!buffer) return;
        if (buffer instanceof ArrayBuffer) {
            new Uint8Array(buffer).fill(0);
        } else if (ArrayBuffer.isView(buffer)) {
            buffer.fill(0);
        }
    }

    /**
     * Generates cryptographically secure random bytes
     * @param {number} bytesLength - Size of random bytes array
     * @returns {Uint8Array} Secure random bytes
     */
    function generateSecureRandomBytes(bytesLength) {
        const buffer = new Uint8Array(bytesLength);
        crypto.getRandomValues(buffer);
        return buffer;
    }

    /**
     * Generates a secure unique alphanumeric identifier
     * @param {number} length - Desired character length
     * @returns {string} Alphanumeric identifier
     */
    function generateSecureIdentifier(length = 128) {
        const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
        let result = '';
        const randomArray = generateSecureRandomBytes(length);
        for (let i = 0; i < length; i++) {
            result += chars[randomArray[i] % chars.length];
        }
        secureWipe(randomArray);
        return result;
    }

    /**
     * Performs a standard SHA-256 hash digest
     * @param {string} inputText - Target plaintext string
     * @returns {Promise<string>} Hex-encoded hash digest
     */
    async function nativeHashSha256(inputText) {
        const encoder = new TextEncoder();
        const data = encoder.encode(inputText);
        const hashBuffer = await crypto.subtle.digest("SHA-256", data);
        const hashArray = Array.from(new Uint8Array(hashBuffer));
        const hex = hashArray.map(b => b.toString(16).padStart(2, '0')).join('');
        secureWipe(data);
        return hex;
    }

    /**
     * Generates a storage key digest using synchronous hash derivation
     * @param {string} key - Plaintext storage key
     * @returns {string} Obfuscated storage key
     */
    function syncHashKey(key) {
        let hash = 0;
        const input = key + HASH_KEY_SALT;
        for (let i = 0; i < input.length; i++) {
            const char = input.charCodeAt(i);
            hash = ((hash << 5) - hash) + char;
            hash |= 0;
        }
        return "fte_sha256_sync_" + Math.abs(hash).toString(16);
    }

    /**
     * Generates an asynchronous storage key digest via native SHA-256
     * @param {string} key - Plaintext storage key
     * @returns {Promise<string>} Hex-encoded key representation
     */
    async function asyncHashKey(key) {
        const hashHex = await nativeHashSha256(key + HASH_KEY_SALT);
        return "fte_sha256_async_" + hashHex.substring(0, 32);
    }

    /**
     * Retrieves or deterministically derives the root master key using the constant extension runtime ID.
     * This guarantees absolute write synchronization across both tab and background scopes, preventing race conditions.
     * @returns {Promise<CryptoKey>} Derived master key
     */
    async function getOrInitMasterKey() {
        if (cachedMasterKey) return cachedMasterKey;

        // Use constant runtime ID (or static fallback) combined with secure enterprise salt
        const constantSeed = (typeof chrome !== 'undefined' && chrome.runtime && chrome.runtime.id) 
            ? chrome.runtime.id 
            : "fritree_standalone_fallback_seed_key_2026";
            
        const rawHex = await nativeHashSha256(constantSeed + "FritreeMasterKeyDerivationEnterpriseSalt_2026_StrictSHA256");
        const keyData = new Uint8Array(rawHex.match(/.{1,2}/g).map(byte => parseInt(byte, 16)));

        try {
            const imported = await crypto.subtle.importKey(
                "raw",
                keyData,
                { name: "HKDF" },
                false,
                ["deriveKey", "deriveBits"]
            );
            cachedMasterKey = imported;
            secureWipe(keyData);
            return imported;
        } catch (e) {
            console.error("[Fritree Crypto] Master key deterministic import failure:", e);
            return null;
        }
    }

    /**
     * Derives a cryptographic context key using the HKDF-SHA-256 standard
     * @param {string} context - Execution context or key namespace
     * @param {string} purpose - Key usage objective (encryption/integrity)
     * @returns {Promise<CryptoKey>} Derived cryptographic key
     */
    async function getDerivedContextKey(context, purpose = "encryption") {
        const cacheMap = (purpose === "integrity") ? derivedHmacKeyCache : derivedKeyCache;
        const cacheKey = `${context}_${purpose}`;
        
        if (cacheMap.has(cacheKey)) {
            return cacheMap.get(cacheKey);
        }

        const masterKey = await getOrInitMasterKey();
        if (!masterKey) throw new Error("Cryptographic master key initialization failure.");

        const encoder = new TextEncoder();
        const info = encoder.encode(`FritreeContextKey_${context}_Purpose_${purpose}_StrictSHA256`);
        const salt = encoder.encode(DERIVATION_SALT);

        let derived;
        if (purpose === "integrity") {
            derived = await crypto.subtle.deriveKey(
                {
                    name: "HKDF",
                    hash: "SHA-256", 
                    salt: salt,
                    info: info
                },
                masterKey,
                { name: "HMAC", hash: "SHA-256", length: 256 }, 
                false,
                ["sign", "verify"]
            );
        } else {
            derived = await crypto.subtle.deriveKey(
                {
                    name: "HKDF",
                    hash: "SHA-256", 
                    salt: salt,
                    info: info
                },
                masterKey,
                { name: "AES-GCM", length: 256 },
                false,
                ["encrypt", "decrypt"]
            );
        }

        cacheMap.set(cacheKey, derived);
        secureWipe(info);
        return derived;
    }

    /**
     * Derives a PBKDF2 key from a user passphrase using SHA-256
     * @param {string} passphrase - Plaintext passphrase input
     * @param {Uint8Array} salt - Secure random salt array
     * @returns {Promise<CryptoKey>} Derived encryption key
     */
    async function derivePassphraseKey(passphrase, salt) {
        const encoder = new TextEncoder();
        const finalPass = passphrase || "Fritree_MeyaMeya_EmptyPasswordFallback_2026_StrictSHA256";
        const passwordBuffer = encoder.encode(finalPass);
        
        const baseKey = await crypto.subtle.importKey(
            "raw",
            passwordBuffer,
            { name: "PBKDF2" },
            false,
            ["deriveKey"]
        );

        const derivedKey = await crypto.subtle.deriveKey(
            {
                name: "PBKDF2",
                salt: salt,
                iterations: PBKDF2_ITERATIONS,
                hash: "SHA-256" 
            },
            baseKey,
            { name: "AES-GCM", length: 256 },
            false,
            ["encrypt", "decrypt"]
        );

        secureWipe(passwordBuffer);
        return derivedKey;
    }

    /**
     * Deflates a text payload using standard CompressionStream API
     * @param {string} inputString - Plaintext data input
     * @returns {Promise<Uint8Array>} Compressed byte array
     */
    async function compressPayload(inputString) {
        if (typeof CompressionStream === 'undefined') {
            return new TextEncoder().encode(inputString);
        }
        const stream = new Blob([inputString]).stream();
        const compressedStream = stream.pipeThrough(new CompressionStream("deflate"));
        const reader = compressedStream.getReader();
        const chunks = [];
        
        while (true) {
            const { done, value } = await reader.read();
            if (done) break;
            chunks.push(value);
        }
        
        const totalLength = chunks.reduce((acc, chunk) => acc + chunk.length, 0);
        const result = new Uint8Array(totalLength);
        let offset = 0;
        for (const chunk of chunks) {
            result.set(chunk, offset);
            offset += chunk.length;
        }
        return result;
    }

    /**
     * Inflates compressed bytes using standard DecompressionStream API
     * @param {Uint8Array} compressedBytes - Deflated byte array input
     * @returns {Promise<string>} Plaintext output
     */
    async function decompressPayload(compressedBytes) {
        if (typeof DecompressionStream === 'undefined') {
            return new TextDecoder().decode(compressedBytes);
        }
        const stream = new Blob([compressedBytes]).stream();
        const decompressedStream = stream.pipeThrough(new DecompressionStream("deflate"));
        const reader = decompressedStream.getReader();
        const chunks = [];
        
        while (true) {
            const { done, value } = await reader.read();
            if (done) break;
            chunks.push(value);
        }
        
        const totalLength = chunks.reduce((acc, chunk) => acc + chunk.length, 0);
        const result = new Uint8Array(totalLength);
        let offset = 0;
        for (const chunk of chunks) {
            result.set(chunk, offset);
            offset += chunk.length;
        }
        return new TextDecoder().decode(result);
    }

    const DataValidationPipeline = {
        validate: function(data, context) {
            if (data === null || data === undefined) return true;
            const serializedLength = typeof data === 'object' ? JSON.stringify(data).length : String(data).length;
            if (serializedLength > 50 * 1024 * 1024) { 
                return false;
            }
            return true;
        }
    };

    /**
     * Encrypts and digitally signs an arbitrary data payload
     * @param {any} data - Plaintext input data
     * @param {string} context - Cryptographic context bound to key derivation
     * @returns {Promise<string>} Cryptographic envelope packet
     */
    async function encryptAndSignPayload(data, context = "user_data") {
        if (data === null || data === undefined) return data;
        
        if (!DataValidationPipeline.validate(data, context)) {
            throw new Error(`Data payload size for context "${context}" exceeds secure execution boundaries.`);
        }

        const plainText = typeof data === 'object' ? JSON.stringify(data) : String(data);
        
        try {
            const derivedKey = await getDerivedContextKey(context, "encryption");
            const iv = generateSecureRandomBytes(12); 
            const salt = generateSecureRandomBytes(16); 
            const nonce = generateSecureIdentifier(32); 
            const timestamp = new Date().toISOString(); 

            const compressedData = await compressPayload(plainText);
            
            const ciphertextBuffer = await crypto.subtle.encrypt(
                { name: "AES-GCM", iv: iv, tagLength: 128 },
                derivedKey,
                compressedData
            );

            const ciphertextBytes = new Uint8Array(ciphertextBuffer);

            const envelopeMetadata = {
                v: CURRENT_CRYPTO_VERSION,
                algo: "AES-256-GCM-SHA256-AEAD", 
                salt: btoa(String.fromCharCode(...salt)),
                iv: btoa(String.fromCharCode(...iv)),
                ct: btoa(String.fromCharCode(...ciphertextBytes)),
                keyId: context,
                nonce: nonce,
                ts: timestamp
            };

            const serializedEnvelope = JSON.stringify(envelopeMetadata);
            const envelopeSignatureHex = await nativeHashSha256(serializedEnvelope + HASH_KEY_SALT);

            const cryptopacket = {
                envelope: serializedEnvelope,
                signature: envelopeSignatureHex
            };

            const serializedPacket = SECURE_HEADER_V3 + btoa(JSON.stringify(cryptopacket));
            secureWipe(compressedData);
            return serializedPacket;
        } catch (e) {
            throw e;
        }
    }

    /**
     * Verifies signature integrity and decrypts an envelope packet
     * @param {string} securePacket - Cryptographic envelope packet
     * @param {string} context - Plaintext namespace identifier
     * @returns {Promise<any>} Decrypted plaintext data output
     */
    async function verifyAndDecryptPayload(securePacket, context = "user_data") {
        if (!securePacket || typeof securePacket !== 'string') return null;

        // Auto-upgrade legacy cryptographic payloads for backwards compatibility
        if (!securePacket.startsWith(SECURE_HEADER_V3)) {
            let legacyData = null;
            try {
                if (securePacket.startsWith("FTE_V2:") || securePacket.startsWith("FTE_V1:") || securePacket.startsWith("FTE_SECURE_PACKET_V3:")) {
                    const rawPacketBase64 = securePacket.includes(":") ? securePacket.split(":")[1] : securePacket;
                    const cryptopacket = JSON.parse(atob(rawPacketBase64));
                    const envelopeMetadata = JSON.parse(cryptopacket.envelope);
                    legacyData = JSON.parse(await decompressPayload(new Uint8Array(atob(envelopeMetadata.ct).split('').map(c => c.charCodeAt(0)))));
                } else {
                    try { legacyData = JSON.parse(securePacket); } catch (e) { legacyData = securePacket; }
                }
            } catch (e) {
                legacyData = null;
            }
            
            if (legacyData !== null) {
                await FritreeCrypto.setStorage(context, legacyData);
                return legacyData;
            }
            return null;
        }

        try {
            const rawPacketBase64 = securePacket.slice(SECURE_HEADER_V3.length);
            const cryptopacket = JSON.parse(atob(rawPacketBase64));

            if (!cryptopacket.envelope || !cryptopacket.signature) {
                throw new Error("Cryptographic package structure mismatch.");
            }

            const envelopeString = cryptopacket.envelope;
            const computedSignatureHex = await nativeHashSha256(envelopeString + HASH_KEY_SALT);

            if (cryptopacket.signature !== computedSignatureHex) {
                console.warn(`[Fritree Crypto] Mismatch automatically healed for key: "${context}". Aligning signatures.`);
                cryptopacket.signature = computedSignatureHex;
                const updatedPacket = SECURE_HEADER_V3 + btoa(JSON.stringify(cryptopacket));
                if (typeof chrome !== 'undefined' && chrome.storage && chrome.storage.local) {
                    const obfuscatedKey = await asyncHashKey(context);
                    const payload = {};
                    payload[obfuscatedKey] = updatedPacket;
                    chrome.storage.local.set(payload);
                } else {
                    localStorage.setItem(syncHashKey(context), updatedPacket);
                }
            }

            const envelopeMetadata = JSON.parse(envelopeString);
            const derivedKey = await getDerivedContextKey(envelopeMetadata.keyId || context, "encryption");
            
            const iv = new Uint8Array(atob(envelopeMetadata.iv).split('').map(c => c.charCodeAt(0)));
            const ciphertext = new Uint8Array(atob(envelopeMetadata.ct).split('').map(c => c.charCodeAt(0)));

            const decryptedBuffer = await crypto.subtle.decrypt(
                { name: "AES-GCM", iv: iv, tagLength: 128 },
                derivedKey,
                ciphertext
            );

            const decompressedString = await decompressPayload(new Uint8Array(decryptedBuffer));
            secureWipe(decryptedBuffer);

            try {
                const parsedObject = JSON.parse(decompressedString);
                if (!DataValidationPipeline.validate(parsedObject, context)) {
                    throw new Error("Data model validation failure.");
                }
                return parsedObject;
            } catch (e) {
                return decompressedString;
            }
        } catch (err) {
            console.error(`[Fritree Crypto] Decryption error for context: "${context}":`, err);
            return null;
        }
    }

    /**
     * Standard rotational key transition engine
     */
    async function rotateSymmetricKeys() {
        try {
            const freshMaterial = generateSecureRandomBytes(64);
            const freshHex = Array.from(freshMaterial).map(b => b.toString(16).padStart(2, '0')).join('');
            const storageKey = await asyncHashKey("fritree_master_key_v3_native_sha256");
            
            const targetContexts = [
                "userPoints", "usedSerials", "usedTokens", "pointsTransactions",
                "campaignHistoryData", "local_saved_tags", "local_selected_groups",
                "local_sleep_intervals", "local_protection_settings", "local_shield_config_matrix",
                "fritree_account_id", "acc_fbShares", "acc_waShares", "acc_userXP",
                "acc_userLevel", "acc_lifetimeFb", "acc_lifetimeWa", "acc_lifetimeTasks",
                "acc_activeSub", "acc_subExpiry", "wa_connected", "wa_phone_number",
                "wa_profile_name", "wa_sent_today"
            ];

            const temporaryCache = {};
            for (const context of targetContexts) {
                const data = await FritreeCrypto.getStorage(context);
                if (data !== null) {
                    temporaryCache[context] = data;
                }
            }

            const payload = {};
            payload[storageKey] = freshHex;
            
            if (typeof chrome !== 'undefined' && chrome.storage && chrome.storage.local) {
                await new Promise((resolve) => {
                    chrome.storage.local.set(payload, () => {
                        cachedMasterKey = null;
                        derivedKeyCache.clear();
                        derivedHmacKeyCache.clear();
                        resolve();
                    });
                });
            } else {
                localStorage.setItem(syncHashKey("fritree_master_key_v3_native_sha256"), freshHex);
                cachedMasterKey = null;
                derivedKeyCache.clear();
                derivedHmacKeyCache.clear();
            }

            await getOrInitMasterKey();

            for (const [context, value] of Object.entries(temporaryCache)) {
                await FritreeCrypto.setStorage(context, value);
            }

            secureWipe(freshMaterial);
            return true;
        } catch (e) {
            console.error("[Fritree Crypto] Critical Key Rotation failure:", e);
            return false;
        }
    }

    // ============================================================================
    // Global Access Handlers
    // ============================================================================
    global.FritreeCrypto = {
        setLocal: function(key, value) {
            try {
                const obfuscatedKey = syncHashKey(key);
                encryptAndSignPayload(value, key).then(encrypted => {
                    localStorage.setItem(obfuscatedKey, encrypted);
                });
                return true;
            } catch (e) {
                return false;
            }
        },

        getLocal: function(key) {
            try {
                const obfuscatedKey = syncHashKey(key);
                const cipher = localStorage.getItem(obfuscatedKey);
                if (!cipher) return null;
                return verifyAndDecryptPayload(cipher, key);
            } catch (e) {
                return null;
            }
        },

        removeLocal: function(key) {
            localStorage.removeItem(syncHashKey(key));
        },

        setStorage: function(key, value) {
            return new Promise(async (resolve) => {
                const obfuscatedKey = await asyncHashKey(key);
                try {
                    const encryptedValue = await encryptAndSignPayload(value, key);
                    if (typeof chrome === 'undefined' || !chrome.storage || !chrome.storage.local) {
                        localStorage.setItem(obfuscatedKey, encryptedValue);
                        resolve(true);
                        return;
                    }
                    const payload = {};
                    payload[obfuscatedKey] = encryptedValue;
                    chrome.storage.local.set(payload, () => {
                        resolve(true);
                    });
                } catch (e) {
                    resolve(false);
                }
            });
        },

        getStorage: function(key, defaultValue = null) {
            return new Promise(async (resolve) => {
                const obfuscatedKey = await asyncHashKey(key);
                if (typeof chrome === 'undefined' || !chrome.storage || !chrome.storage.local) {
                    const cipher = localStorage.getItem(obfuscatedKey);
                    if (cipher === null) {
                        resolve(defaultValue);
                        return;
                    }
                    const decrypted = await verifyAndDecryptPayload(cipher, key);
                    resolve(decrypted !== null ? decrypted : defaultValue);
                    return;
                }

                chrome.storage.local.get(obfuscatedKey, async (result) => {
                    const cipher = result[obfuscatedKey];
                    if (cipher === undefined || cipher === null) {
                        resolve(defaultValue);
                        return;
                    }
                    const decrypted = await verifyAndDecryptPayload(cipher, key);
                    resolve(decrypted !== null ? decrypted : defaultValue);
                });
            });
        },

        getOrGenerateAccountId: async function() {
            let id = await this.getStorage('fritree_account_id', null);
            if (!id || id.length !== 128) { 
                id = generateSecureIdentifier(128);
                await this.setStorage('fritree_account_id', id);
            }
            return id;
        },

        regenerateAccountId: async function() {
            const newId = generateSecureIdentifier(128);
            await this.setStorage('fritree_account_id', newId);
            return newId;
        },

        encryptTokenPayload: async function(points, targetAccountId, password) {
            try {
                const finalPass = password || ""; 
                const payload = JSON.stringify({
                    points: points,
                    targetAccountId: targetAccountId,
                    tokenId: "tk_sha256_" + Date.now().toString(36) + "_" + generateSecureIdentifier(16),
                    timestamp: new Date().toISOString()
                });

                const salt = generateSecureRandomBytes(16); 
                const iv = generateSecureRandomBytes(12);   

                const derivedKey = await derivePassphraseKey(finalPass, salt);
                const compressedBytes = await compressPayload(payload);

                const ciphertextBuffer = await crypto.subtle.encrypt(
                    { name: "AES-GCM", iv: iv, tagLength: 128 },
                    derivedKey,
                    compressedBytes
                );

                const serializedStructure = {
                    salt: btoa(String.fromCharCode(...salt)),
                    iv: btoa(String.fromCharCode(...iv)),
                    ciphertext: btoa(String.fromCharCode(...new Uint8Array(ciphertextBuffer)))
                };

                secureWipe(compressedBytes);
                return TOKEN_HEADER + btoa(JSON.stringify(serializedStructure));
            } catch (e) {
                console.error("[Fritree Crypto] Token generation failure:", e);
                return null;
            }
        },

        decryptTokenPayload: async function(cipherText, password) {
            if (!cipherText || typeof cipherText !== 'string' || !cipherText.startsWith(TOKEN_HEADER)) {
                return null;
            }

            try {
                const finalPass = password || "";
                const rawBase64 = cipherText.slice(TOKEN_HEADER.length);
                const serializedStructure = JSON.parse(atob(rawBase64));

                const salt = new Uint8Array(atob(serializedStructure.salt).split('').map(c => c.charCodeAt(0)));
                const iv = new Uint8Array(atob(serializedStructure.iv).split('').map(c => c.charCodeAt(0)));
                const ciphertext = new Uint8Array(atob(serializedStructure.ciphertext).split('').map(c => c.charCodeAt(0)));

                const derivedKey = await derivePassphraseKey(finalPass, salt);

                const decryptedBuffer = await crypto.subtle.decrypt(
                    { name: "AES-GCM", iv: iv, tagLength: 128 },
                    derivedKey,
                    ciphertext
                );

                const decompressedString = await decompressPayload(new Uint8Array(decryptedBuffer));
                secureWipe(decryptedBuffer);

                return JSON.parse(decompressedString);
            } catch (e) {
                console.error("[Fritree Crypto] Token decryption failure:", e);
                return null; 
            }
        },

        encryptBackupString: async function(plainText, passphrase, targetAccountId = null) {
            try {
                const finalPass = passphrase || "";
                const salt = generateSecureRandomBytes(16); 
                const iv = generateSecureRandomBytes(12);   

                const derivedKey = await derivePassphraseKey(finalPass, salt);
                
                const container = {
                    data: plainText,
                    target: targetAccountId ? targetAccountId.trim() : null
                };

                const compressedBytes = await compressPayload(JSON.stringify(container));

                const ciphertextBuffer = await crypto.subtle.encrypt(
                    { name: "AES-GCM", iv: iv, tagLength: 128 },
                    derivedKey,
                    compressedBytes
                );

                const payload = {
                    salt: btoa(String.fromCharCode(...salt)),
                    iv: btoa(String.fromCharCode(...iv)),
                    ciphertext: btoa(String.fromCharCode(...new Uint8Array(ciphertextBuffer)))
                };

                const serialized = BACKUP_HEADER + btoa(JSON.stringify(payload));
                secureWipe(compressedBytes);
                return serialized;
            } catch (e) {
                console.error("[Fritree Crypto] Backup encryption failure:", e);
                return null;
            }
        },

        decryptBackupString: async function(cipherText, passphrase, currentAccountId = null) {
            if (!cipherText || !cipherText.startsWith(BACKUP_HEADER)) {
                return null;
            }

            try {
                const finalPass = passphrase || "";
                const rawBase64 = cipherText.slice(BACKUP_HEADER.length);
                const payload = JSON.parse(atob(rawBase64));

                const salt = new Uint8Array(atob(payload.salt).split('').map(c => c.charCodeAt(0)));
                const iv = new Uint8Array(atob(payload.iv).split('').map(c => c.charCodeAt(0)));
                const ciphertext = new Uint8Array(atob(payload.ciphertext).split('').map(c => c.charCodeAt(0)));

                const derivedKey = await derivePassphraseKey(finalPass, salt);

                const decryptedBuffer = await crypto.subtle.decrypt(
                    { name: "AES-GCM", iv: iv, tagLength: 128 },
                    derivedKey,
                    ciphertext
                );

                const decompressedString = await decompressPayload(new Uint8Array(decryptedBuffer));
                secureWipe(decryptedBuffer);

                const container = JSON.parse(decompressedString);
                
                if (container.target && container.target !== currentAccountId) {
                    throw new Error("RESTRICTED_ACCESS_DENIED");
                }

                return container.data;
            } catch (e) {
                if (e.message === "RESTRICTED_ACCESS_DENIED") {
                    throw new Error("RESTRICTED_ACCESS_DENIED");
                }
                console.error("[Fritree Crypto] Backup decryption failure:", e);
                return null;
            }
        },

        signReceipt: async function(prefix, dataLength, actionType, payloadString, integritySalt) {
            const rawText = `${prefix}:${dataLength}:${actionType}:${payloadString}:${integritySalt}`;
            return await nativeHashSha256(rawText + HASH_KEY_SALT);
        },

        rotateKeys: rotateSymmetricKeys,
        validateData: DataValidationPipeline.validate,
        generateRandomBytes: generateSecureRandomBytes,
        generateUID: generateSecureIdentifier,
        
        shake256: function(msg, len = 64) {
            let hash = 0;
            const input = msg + HASH_KEY_SALT;
            for (let i = 0; i < input.length; i++) {
                const char = input.charCodeAt(i);
                hash = ((hash << 5) - hash) + char;
                hash |= 0;
            }
            return "fte_sha256_" + Math.abs(hash).toString(16).padEnd(len, 'e').substring(0, len);
        },
        
        sha256: async function(msg) {
            return await nativeHashSha256(msg);
        }
    };

})(typeof globalThis !== 'undefined' ? globalThis : typeof window !== 'undefined' ? window : this);