What AES-256-GCM does in Strumio

Separate the algorithm name into its parts

AES is a standardized symmetric block cipher, 256 identifies the key length used here, and GCM is Galois/Counter Mode. Symmetric means the same secret key is needed for encryption and decryption. GCM turns the cipher into an authenticated-encryption construction suitable for protecting content and detecting unauthorized changes.

A longer key is not a statement that every surrounding component is equally strong. Random generation, nonce handling, key delivery, endpoint security, authentication, software updates, and user behavior determine the real system. Security claims should describe the complete flow rather than treating an algorithm label as a guarantee.

Use authentication as well as confidentiality

Encryption makes content unreadable without the key. GCM also produces an authentication tag checked during decryption. If ciphertext, relevant parameters, or the tag are changed, correct implementations reject decryption instead of returning plausibly altered plaintext. This helps detect corruption and tampering with the encrypted payload.

The authentication tag does not identify a real-world sender. Anyone with the correct key can create valid encrypted content, and unsafe files remain unsafe after valid decryption. Verify people and expected files through separate trusted context when authenticity matters.

Generate keys and nonces in the browser

Strumio relies on the Web Crypto API rather than asking users to invent encryption keys. Random key material is created locally, and encryption occurs before protected content is uploaded. Each operation also needs an appropriate nonce or initialization value; nonce reuse under one GCM key can undermine security.

These implementation details are why copying pieces into custom scripts or manually reusing values is risky. Use the supported flow on an updated browser. The service still processes encrypted payloads and operational delivery records, while the complete link carries key material in a fragment for recipient-side decryption.

Protect the key and plaintext endpoints

Strong ciphertext is useful only while the key remains controlled. A complete Strumio URL is sensitive because the URL fragment contains the random decryption key. Anyone who obtains the complete link may be able to attempt access while the item remains available, subject to its password and delivery controls.

Plaintext exists on the sender before encryption and recipient after decryption. Malware, extensions, screen capture, clipboard history, and intentional copying are outside AES-GCM's protection. Use trusted endpoints, verify recipients, and rotate underlying credentials when disclosure would continue to grant access.

Combine cryptography with delivery controls

One-time access can atomically limit an encrypted payload to one successful retrieval, and expiration limits the retrieval window. Optional passwords add a separate access check when delivered independently. None of these controls can erase plaintext already seen or prove that the first viewer was the intended person.

Use AES-256-GCM browser encryption as one layer in a risk-aware handoff. Individual accounts, least privilege, managed secret storage, revocation, monitoring, backups, and incident response remain necessary for long-term operations and high-impact credentials.

Related guidance

• See where browser encryption occurs
• Understand key delivery in URL fragments
• Review Strumio's implemented controls
• Browse all secure sharing guides