RSA Verify Signature Online
Verify the authenticity of an RSA digital signature using the signer's public key. Paste the public key, original message, and signature — the tool will confirm whether the signature is valid (message is authentic and unaltered) or invalid. Supports PKCS#1 v1.5 and RSA-PSS. Runs entirely in the browser.
What Verification Confirms
- Authenticity: The message was signed by the holder of the matching private key
- Integrity: The message content has not been modified since signing
- Non-repudiation: The signer cannot deny having signed the message (if the private key was kept secure)
Verification Checklist
- Use the correct public key (matching the signer's private key)
- Paste the exact original message — any whitespace or encoding difference causes failure
- Match the signing algorithm (PKCS#1 v1.5 or RSA-PSS)
- Match the hash algorithm (SHA-256, SHA-384, or SHA-512)
- Use the correct signature encoding (base64 or hex)
Common Applications
- Verifying JWT signatures (RS256 = PKCS#1 v1.5, PS256 = RSA-PSS)
- Checking software or document authenticity
- Validating signed API responses
- Testing RSA signing implementations
Frequently Asked Questions
What does "signature valid" mean?
A valid signature confirms two things: (1) the message was signed by the owner of the corresponding private key — proving authenticity, and (2) the message has not been modified since it was signed — proving integrity. If even a single character of the message changes, the signature becomes invalid.
What does "signature invalid" mean?
An invalid result means one or more of: the wrong public key was used (the public key does not match the private key that created the signature), the message content has been modified, the signature itself is corrupted or incomplete, the algorithm or hash does not match what was used during signing.
Does verification reveal anything about the private key?
No. Signature verification only uses the public key, which is meant to be shared. The private key is not involved and cannot be derived from verification. This is what makes RSA signatures useful — verification is open to anyone.
Why does RSA-PSS verification fail for a valid PKCS#1 v1.5 signature?
PKCS#1 v1.5 and RSA-PSS use different padding schemes and are not interchangeable. Always use the same algorithm for signing and verifying. If you used PKCS#1 v1.5 to sign (or vice versa), make sure to select the matching algorithm in the verifier.
Can I verify a signature created by OpenSSL or other tools?
Yes. As long as the signature was created with RSA (PKCS#1 v1.5 or RSA-PSS) using a compatible key and hash, this tool can verify it. The public key must be in SPKI PEM format (BEGIN PUBLIC KEY). OpenSSL exports public keys in this format with: openssl rsa -pubout -in private.pem -out public.pem
Does changing the message by a single character invalidate the signature?
Yes. The signature is computed over the hash of the exact message content. Any change — even adding a space or changing capitalization — produces a completely different hash, and the signature will not verify. This is the fundamental integrity guarantee of digital signatures.