That number is not 64-bit long. It is 64 hexadecimal characters long, which would be 64*8 = 512 bits!
To create a 64-character random string:
characters = ['0':'9', 'A':'F']; %list of characters allowed in the string
randstring = characters(randi(numel(characters), 1, 64))
Note that it is not possible to store a 512-bit number in base matlab other than as a string.
.png)
