windowcryptosubtle

Windowcryptosubtle refers to the SubtleCrypto interface exposed by the Web Crypto API as window.crypto.subtle in web browsers. It is a programmatic, browser-based interface that enables cryptographic operations within web pages while controlling exposure of key material through CryptoKey objects and usage constraints. The API is available in secure contexts and is designed to operate asynchronously, returning Promises for most operations.

Typical operations include generateKey, importKey, exportKey, encrypt, decrypt, sign, verify, digest, deriveKey, and deriveBits. Keys are represented by CryptoKey objects and may be marked extractable or non-extractable, with allowed usages restricted by the key's configuration. All methods return Promises, reflecting their asynchronous nature and the need to avoid long blocking operations in the browser.

Algorithms supported by windowcryptosubtle cover both symmetric and asymmetric cryptography, including AES-GCM and AES-CBC (with AES-GCM preferred for modern use), RSA-OAEP, RSASSA-PKCS1v1_5, ECDSA, and ECDH, along with standard hash functions such as SHA-256, SHA-384, and SHA-512. While some legacy options exist, SHA-1 is generally deprecated in contemporary use.

Usage pattern typically involves obtaining a CryptoKey via generateKey or importKey, then invoking encrypt/decrypt or sign/verify with detailed algorithm parameters and data provided as ArrayBuffer or typed arrays. The results are usually ArrayBuffer values or, in some cases, CryptoKey objects, with operation outcomes delivered through resolved Promises.

Security and scope considerations include the requirement of a secure context (HTTPS or localhost) and adherence to browser security policies. SubtleCrypto is designed to minimize exposure of sensitive data, but developers must follow best practices for key management, including careful handling of extractable keys and appropriate key usages. It is a core, standards-based facility for client-side cryptography in web applications.