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Let's assume this scenario:

  1. I sign a message using my subkey
  2. I send the signed message to someone who has my master public key

Is recipient be able to verify my message? Or do I have to provide my public-subkey?

2 Answers 2

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You have to provide the public subkey to the recipient in order for them to validate anything signed with the corresponding private subkey.

The Master key serves a purpose somewhat analogous to a Certificate Authority. It represents your authority to bless all your personal subkeys as valid keys that were issued by you. But just as having a root certificate doesn't mean you can use TLS to talk to any random server that was issued a public key - you still need that server's public key (which is delivered on the certificate.)

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Digital signature is equivalent to handwritten signature where the authenticity of the person is assured (digital signature is the virtual equivalent of a written signature). It works as explained below:

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  1. Signer creates a digest of the message — kind of digital fingerprint. If the message/content changes, the digest also will change.
  2. Signer then encrypts the digest with his private key. The encrypted digest is called the digital signature.
  3. The encrypted digest is sent to Verifier along with the message.
  4. When Verifier receives the message, he decrypts the digest using Signer's public key.
  5. Verifier then creates a digest of the message using the same function that Signer used.
  6. Verifier compares the digest that he created with the one that Signer encrypted. If the digests match, then Verifier can be confident that the signed message is indeed from Signer. If they don't match, then the message has been modified or not from Signer.

You mat refer these sources: https://searchsecurity.techtarget.com/answer/Which-private-keys-and-public-keys-can-create-a-digital-signature

https://medium.com/@meruja/digital-signature-generation-75cc63b7e1b4

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  • Not only does this not mention subkeys which is what the question is actually about, "encryption of hash" is a misleading description of signing. Aug 4, 2018 at 4:04

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