Key pairs and digital signitures

Features
1

Hi

I am struggling to grasp a certain part of digital signatures. In the white paper it says this

"To facilitate this, person A
can hash the message M and then decrypt it using their private
key; the result of these operations is called the digital signature
of the message "

How can you hash the message and the decrypt it. Surely its not been encrypted yet to decrypt. Is this a typo or am i missing something?

2

Not sure which paper you are reading, but a dig signature is really a mechanism like:

  1. Hash message
  2. Encrypt hash with your private key

To validate a doc is signed then a reader

  1. Hash the doc
  2. Decrypt the signature with the senders public key and compare that with the above hash.

They come in 2 forms usually,

  1. The sig is appended to the doc (so you strip that before hash check)
  2. The sig is separate from the doc (wwe use this part a lot).

So signing is opposite of encrypt really in asymmetric world, where you encrypt data with the receiver’s public key and send to them. So signing is really encryption, this is the only encryption in bitcoin really, this signature part.

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3

Thanks @dirvine . I think its a typo in the public key infrastructure white paper. Its says decrypt when it means encrypt and vise versa.

Edit.

I can sleep easy now.

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