Digital Signature — Sign & Verify

A digital signature is a cryptographic technique that verifies the authenticity and integrity of a digital message. It uses a private key to create the signature and a corresponding public key to verify it. Digital signatures provide three key properties: authentication (who signed it), integrity (the message hasn't been altered), and non-repudiation (the signer cannot deny signing).

Yes. All cryptographic operations are performed entirely within your browser using the Web Crypto API. Your private key is generated and stored only in the browser's memory (RAM) and is never transmitted to any server. When you close the tab or clear your keys, the key material is gone. For maximum security, use this tool on a trusted device and clear your keys after use.

RSA (Rivest-Shamir-Adleman) is the most widely supported algorithm, with key sizes typically ranging from 2048 to 4096 bits. It produces larger signatures but has decades of proven security. ECDSA (Elliptic Curve Digital Signature Algorithm) uses elliptic curve cryptography, offering equivalent security with much smaller key sizes (e.g., a 256-bit ECDSA key provides security comparable to a 3072-bit RSA key). ECDSA signatures are also shorter, making them ideal for bandwidth-constrained applications like blockchain and mobile.

SHA-256 is the industry standard and recommended for most use cases. It offers an excellent balance of security and performance. SHA-384 and SHA-512 provide higher security margins and are sometimes required for compliance with certain standards (e.g., some government applications). All three are considered secure as of today. Avoid SHA-1, which is deprecated and not supported by this tool.

RSASSA-PKCS1-v1_5 is the traditional RSA signature scheme, widely supported across all platforms and legacy systems. RSA-PSS (Probabilistic Signature Scheme) is a newer scheme that offers stronger theoretical security guarantees and is recommended for new applications. However, PKCS1-v1_5 remains secure in practice when implemented correctly. Use PKCS1-v1_5 for maximum compatibility, or RSA-PSS for enhanced security.

Non-repudiation means that once someone signs a message with their private key, they cannot plausibly deny having signed it. Since only the holder of the private key could have produced a valid signature, and the signature can be verified by anyone with the public key, the signer is bound to the signed content. This is a cornerstone of digital contracts, legal documents, and secure communications.

Yes! Once the page is loaded, all operations run entirely in your browser. You can disconnect from the internet and the tool will continue to function normally. No network requests are made during key generation, signing, or verification. This makes the tool ideal for air-gapped or high-security environments.