Hash Reading Assignment’
1. What is the hashing algorithm called used in Bitcoin?
BTC uses SHA-256.
SHA-256 takes an in-deterministic input and changes the output to a prescribed 256 hashed character length. SHA-256 always creates a 256 hashed output regardless of the I/P character length. The resulting hashed 256 output is uniquely encode to the original I/P allowing tracking of the input by simply recording the hashed 256 character O/P.
2. Why is this hashing algorithm really hard (almost impossible) to brute-force?
Using brute force to determine the I/P from the hashed O/P is virtually impossible to deduce because of the following features added to the SHA-256 algorithm;
- Pre-image resistance
SHA-256 hash function ensures mathematically that a small change in the I/P (e.g. changing “abc” to “Abc”) completely changes the hashed 256 O/P character set. This complete change in hashed O/P is an essential criteria to make the I/P very difficult to deduce via brute force means. Not impossible, simply takes too much time to deduce to make the effort value add.
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The “none” (concatenated random number)
To further increase the difficulty level of difficulty the SHA-256 hash function the I/P is concatenated with a random number called the “nonce”. To force the “nonce” to be a truly random number the network forces the resulting SHA-256 hashed O/P to be less than a prescribed number. By forcing this prescribed relationship this ensures the resulting “nonce” is truly random and cannot be guessed further increasing the difficulty level to deduce the I/P via brute force means.
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Collision resistance
To improve collision resistance, no two hashed functions produce the same SHA-256 O/P, blockchain network constantly adjusts the value of the required SHA-256 hashed O/P.
By constantly changing the value of the prescribed hashed O/P ensures the time taken to mathematical solve the value of the “nonce” takes less than 10 minutes to compute, and further reduces the probability that two hashed I/Ps will produce the same hashed functional O/P further increasing the difficulty level to deduce the I/P by brute force means.
