RSA Sign Message
This online tool helps you sign messages using RSA. It supports various signature algorithms. You can also use PEM with a passphrase. Read more
Sign a message with RSA
An RSA signature uses a private key and hash algorithm to create a value that holders of the public key can verify. This tool accepts text or encoded bytes, supports several digest algorithms, and outputs the signature as Hex or Base64.
A signature provides authenticity and integrity when the verifier already trusts the public key. It does not encrypt the message or keep it confidential.
How to create an RSA signature
- Enter the exact message and select its input encoding.
- Choose the signature hash required by the receiving system; SHA-256 is the default.
- Paste the private key and its PEM passphrase when needed.
- Sign, then transmit the message, signature, algorithm identifier, and trusted public-key reference.
Whitespace, line endings, Unicode encoding, and serialization all affect the signed bytes. Define a canonical representation before different systems exchange signatures.
Algorithm compatibility
The verifier must use the same message bytes, RSA public key, digest algorithm, signature scheme, and signature encoding. RFC 8017 defines RSA signature schemes and key representation.
Legacy digest choices remain available for compatibility but should not be selected for a new protocol without a specific requirement and security review.
RSA signing FAQ
Does signing hide the message?
No. Anyone may read an unencrypted message. Encrypt separately when confidentiality is also required.
Can I sign with the public key?
No. Signing requires the private key; the public key verifies the result.
How do I test the signature?
Use RSA Verify Signature with the original message, public key, matching algorithm, and exact signature bytes.