Digital Signature Authentication Made Easy

Which of the following is not one of the functions of a digital signature?

a cryptographic hash allows you to take any amount of data it can be a small bit of text or it can be an entire book and you can represent that bit of data as a short string of text we refer to this short string of hashed text as a message digests a hash is not an encrypted version of the original text it's really a one-way trip there's no way to recover the original text by simply looking at the hashed value it's because of this unique characteristic that we commonly use hashes to store passwords that way we can compare a stored hash against another hash that's given to us later but we'll still have no idea what the original password was from the user we might also use hashes to confirm that a file that we've downloaded is identical to the original version of that file and we use hashing during the creation of a digital signature that allows us to provide authentication non-repudiation and integrity to a particular document a fundamental characteristic of hashing algorithms is that two different messages will not have the exact same hash we call this a hash collision and it's important that we don't have two documents that somehow managed to represent exactly the same hash let's look at the process of creating a hash for this we're going to use the sha-256 hashing algorithm this creates a hash that is 256 bits in length and we usually represent this as something human readable by using 64 hexadecimal characters for this hash we'll take a simple sentence which says my name is professor Messer with a period if we were to perform the sha-256 hash of that text we receive this particular hash value we can also perform the same function with another bit of text this one looks almost identical but instead of having a period at the end I put an exclamation mark and I performed exactly the same sha-256 hash and you can see that the hash value for these is completely different even though the only thing that is different between the two messages is that single piece of information at the end a period or an exclamation mark if we were to compare these two you can see that they are very different from each other even though the original message was very similar the only difference was really the punctuation at the end but because this hashing algorithm is designed to create very different hashes we can see that there is a remarkable difference between one hash and the other this hashing method can be used with any type of message it could be a large graphics file it could be a disk image or it can be a sentence like the one I used in the previous slide we use that hashing algorithm to create that fixed size string which is our message digests this message digests the hash that is created from...