Crypto Angels Space💰🚀

private keys remain private.But private communication is not all Alice and Bob can do. Alice can also cryptographically “sign” any piece of data (and so can Bob). To do so, Alice must mathematically combine her private key with this data. The result will be another seemingly random string of numbers known as the “signature.” Once again, it’s impossible to recreate Alice's private key from the signature (with or without the piece of data). It’s all still a one-way street.The interesting thing about this signature is that Bob (or anyone else) can check it against Alice’s public key. This tells Bob that it was indeed Alice that created the signature with her private key (and the added piece of data). This can, in turn, mean whatever Alice and Bob want. For example, it can mean that Alice agrees with the content of the data (just like a handwritten signature).A blind signature then takes all this one step further. This time, Bob first generates a random number, called a “nonce,” and mathematically combines this with the piece of data. This “scrambles” the piece of data to make it seem like yet another random string of numbers. Bob can then give the scrambled data to Alice for her to sign. Alice cannot tell what the original data looks like, so she is “blind signing” it. The result is a “blind signature.”Now, the interesting thing about this blind signature is that it’s not just linked to Alice’s keys (like any signature would be) and the scrambled data. The same blind signature is also linked to the original, unscrambled data. Using only Alice’s public key, anyone can check that Alice signed a scrambled version of the original data — including, of course, Alice herself, if she does get to see the original data later on.eCashThis blind signature scheme is the trick that Chaum used to create a digital money system.To realize this, Alice from the above example would actually be a bank: Alice Bank. This is a regular bank, like banks exist today, where customers have bank accounts with (in this example) U.S. dollar deposits. Let’s say Alice Bank has four customers: Bob, Carol, Dan and Erin. And let’s say that Bob wants to buy something from Carol.First, Bob requests a “withdrawal” from Alice Bank. (Ideally, he had already made this withdrawal earlier — but never mind that for now.) To make this withdrawal, Bob actually creates “digital banknotes” himself, in the form of unique numbers: “serial numbers.” On top of that, he scrambles these banknotes, as shown above. These scrambled banknotes are sent to Alice Bank. Having received the scrambled banknotes from Bob, Alice Bank then blind signs each scrambled banknote and sends them back to Bob. For each signed, scrambled banknote that she sends back, Alice Bank subtracts one dollar from Bob’s bank account.Now, because Alice Bank blind signed the scrambled banknotes, her signature is also linked to the original, unscrambled banknotes. So, Bob can now use the original, unscrambled banknotes to pay Carol by simply sending them to her.As Carol receives the banknotes, she should forward them to Alice Bank. Alice Bank then checks that she indeed blind signed each of the banknotes, which her blind signatures allow her to do: they are linked to her own keys. Alice Bank also checks that the same banknotes (serial numbers) haven’t already been deposited by someone else in order to ensure that they haven’t been double-spent.As the banknotes check out, Alice Bank adds the equivalent number of dollars to Carol’s bank balance, and lets Carol know. Upon this confirmation, Carol knows she’s been paid valid banknotes by Bob and can safely send him whatever he was buying from her.

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