signatureValue

SignatureValue is the cryptographic output produced when a digital signature is created using a private key. In public-key cryptography, a signer applies a signing algorithm to a representation of the data—often a digest—using their private key, and the resulting signatureValue binds the signer's identity to the data and to the specific version of the message. The value can be used by others to verify that the data originated with the signer and that it has not been altered since signing.

Format and encoding of signatureValue depend on the signature algorithm. For RSA-based signatures, it is typically a binary value representing the signed digest. For ECDSA, the signature is a pair of numbers (r, s) that is encoded into a byte sequence. In XML Digital Signatures, the SignatureValue element contains the base64-encoded bytes of the signer’s signature produced over the canonicalized SignedInfo.

Verification involves applying the signer's public key to the same data or digest and checking that the signatureValue is valid under the chosen algorithm. A valid signature confirms integrity, authenticity, and non-repudiation under the assumption of key control. SignatureValue is typically transmitted with the signed data, and its format must be agreed upon between sender and receiver.

Security considerations include protecting the private key, using appropriate algorithms and key lengths, and proper key management. The signatureValue itself is usually not secret, but exposing it without the data or the public key provides little value. Incorrect encoding or canonicalization can lead to verification failures.