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I have some bytes, and I sign them with my private key using ECDSA. The resultant (71) bytes are the signature.

But what is the name of the bytes I have signed? (If this were encryption, they would be called "plaintext".)

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  • $\begingroup$ Although message can also be used to mean input for other functions or it could be used as a more generic term. So calling it the "message to be signed" or "signed message" would be a good idea in case the context is not sufficiently clear. $\endgroup$ – Maarten - reinstate Monica Nov 4 '15 at 16:31
  • $\begingroup$ When the point is to distinguish the "pre-signature" value (like pre-crime in Minority Report?) it is sometimes labelled "TBS" for "To Be Signed" e.g. X.509/PKIX tools.ietf.org/html/rfc5280#section-4.1 . $\endgroup$ – dave_thompson_085 Dec 27 '15 at 17:51
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The correct term for bytes to be signed is “message”.

Generally, it does not really matter if a message to be signed is human readable or not. Sometimes, you may also find it mentioned as “digital message”… which practically is the same and merely extends the term to explicitly hint at the fact the message is digitally stored and/or processed.

References showing the use of the term can be found at various sources. For example: scientific papers and websites talking about cryptography and/or cryptanalysis in relation to digital signatures.

For your convenience, here are a couple of quotes showing its usage (bold-italic emphasis is mine):

randomly picked, yet well-known websites

randomly picked, yet well-known crypto-related papers

  • source: Identity-based cryptosystems and signature schemes by A Shamir - Advances in cryptology, 1985

    … However, when g is known, there is a very simple way to generate any number of signatures of any message even when the factorization of n is unknown. To sign the message m, the user chooses a random number r …

  • source: A digital signature based on a conventional encryption function by RC Merkle – Advances in Cryptology (CRYPTO'87), 1988

    … If A wishes to sign message m …

  • source: Group signatures by D Chaum, E Van Heyst – Advances in Cryptology (Eurocrypt'91), 1991

    … If person i wants to sign message n, he chooses randomly some set r of persons (including himself); his signature will be … If person i wants to sign message m=An), he randomly chooses …

  • source: The exact security of digital signatures-How to sign with RSA and Rabin by M Bellare, P Rogaway – Advances in Cryptology (Eurocrypt'96), 1996

    … In order to sign message M , the signer first picks a random seed T of length …

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