Chance that first 6 characters of a SHA-1 hash matching another SHA-1 hash? Just what the question says -- what is the chance that the first six characters of a SHA-1 hash will match the first six characters of any given SHA-1 hash?

SHA-1 produces a 120 bit value, no characters.
However, such hashes are often conveyed using a string of fourty hex digits.
The probability of six identical hex digits (assuming with suitable justification uniform distribution) is $\frac1{16^6}$
