AES-256-GCM Browser Encryption — RFC 5116 & NIST SP 800-38D Technical Guide
Encrypt and decrypt text using AES-256-GCM authenticated encryption entirely inside your browser with hardware-accelerated Web Crypto API.
01. AES-GCM Authenticated Encryption: RFC 5116 & NIST SP 800-38D
AES-GCM (Galois/Counter Mode) is an authenticated encryption with associated data (AEAD) scheme standardized in NIST SP 800-38D. Unlike AES-CBC, which only provides confidentiality, AES-GCM simultaneously guarantees data integrity and authenticity through a 128-bit authentication tag appended to every ciphertext.
DevOmniTools uses the W3C Web Cryptography API (SubtleCrypto.encrypt) backed by your operating system's hardware-accelerated AES-NI instruction set. On Intel processors, AES-NI delivers throughput exceeding 10 GB/s, while the authentication tag computation uses the GHASH polynomial function over GF(2^128).
A unique 96-bit Initialization Vector (IV) is generated cryptographically for every encryption operation using crypto.getRandomValues(), satisfying NIST SP 800-38D Section 8.2 requirements for deterministic IV generation safety.
- AES-256-GCM: 256-bit key, 96-bit IV, 128-bit authentication tag per NIST SP 800-38D.
- Web Crypto API: Hardware-accelerated SubtleCrypto.encrypt() with zero JavaScript fallback.
- PBKDF2 Key Derivation: Password-to-key stretching using SHA-256, 100,000 iterations, RFC 2898.
All key derivation, IV generation, encryption, and decryption computations execute entirely in your browser's JavaScript sandbox. No plaintext, ciphertext, or cryptographic key material ever leaves your device.
02. Key Derivation, IV Management & Ciphertext Encoding
When a passphrase is supplied, PBKDF2 (Password-Based Key Derivation Function 2) derives the 256-bit AES key using SHA-256 as the pseudorandom function with a minimum 100,000 iteration count, as recommended by OWASP and aligned with RFC 2898 Section 5.2. A cryptographically random 128-bit salt, unique per operation, prevents rainbow-table precomputation attacks.
The final output concatenates the Base64URL-encoded salt, IV, authentication tag, and ciphertext into a single portable string, ensuring portability across environments while maintaining the integrity verification chain required for authenticated decryption.
- Salt: 128-bit random per PBKDF2 operation — prevents dictionary and rainbow-table attacks.
- IV uniqueness: 96-bit crypto.getRandomValues() — never reused across sessions.
- Output format: Base64URL-encoded salt|IV|tag|ciphertext for safe clipboard and JSON embedding.
03. Common AES Implementation Mistakes & Security Pitfalls
AES-ECB (Electronic Codebook Mode) is cryptographically broken for most data patterns because identical plaintext blocks produce identical ciphertext blocks, leaking structural information. Never use ECB mode for production encryption. AES-GCM eliminates this vulnerability through counter-mode randomization.
IV reuse in AES-GCM is catastrophic: two messages encrypted with the same key and IV allow an attacker to recover the XOR of both plaintexts and forge valid authentication tags. This tool enforces a fresh cryptographically random IV for every single encryption call, making IV collision statistically impossible under 2^96 birthday bound.
- Never reuse IVs: GCM IV collision completely breaks confidentiality and authentication.
- Avoid AES-ECB: Identical plaintext blocks reveal repeating patterns in ciphertext.
- Authentication tag verification: Always verify the GCM tag before processing decrypted data.
Frequently Asked Questions (FAQ)
Is AES-256-GCM encryption safe for sensitive data?
Yes. AES-256-GCM is FIPS 140-3 approved and recommended by NSA Suite B for protecting classified information. The authentication tag prevents ciphertext tampering before decryption.
Does my password or plaintext get sent to any server?
Never. All cryptographic operations run inside your browser using the W3C Web Crypto API. Your data never leaves your device.
What is the maximum data size I can encrypt?
AES-GCM in browsers can handle up to 2^39 minus 256 bits of plaintext per NIST specification. For practical browser use, files up to several hundred megabytes work without UI blocking when processed in Web Workers.
Can I use AES-256 Online Encryption & Decryption Tool (Client-Side) offline without an active internet connection?
Offline use requires the page and its tool assets to finish caching first. Core transformations can then run locally; optional AI and contact delivery require internet.
Is AES-256 Online Encryption & Decryption Tool (Client-Side) free to use with any rate limits or paywalls?
Core tools are free to use without an account. Device memory and tool-specific safety limits apply. Optional AI and online contact services have usage limits.