You can validate that a given password is correct for a given username using the shadow file. On most modern distributions, the hashed passwords are stored in the shadow file /etc/shadow (which is only readable by root). As root, pull the line from the shadow file for the given user like so: cat /etc/shadow | … Read more
In our case, NoMethodErrors due to nil references are by far the most common errors we see in our production environments. The new Hash#dig allows you to omit nil checks when accessing nested elements. Since hashes are best used for when the structure of the data is unknown, or volatile, having official support for this … Read more
An MD5 or SHA1 hash in PHP returns a hexadecimal number, so all you need to do is convert bases. PHP has a function that can do this for you: $bignum = hexdec( md5(“test”) ); or $bignum = hexdec( sha1(“test”) ); PHP Manual for hexdec Since you want a limited size number, you could then … Read more
I prefer tap, as I think it provides a cleaner solution than the ones described here by not requiring any hacky deleting of elements and by clearly defining the scope in which the hash is being built. It also means you don’t need to declare an unnecessary local variable, which I always hate. In case … Read more
.NET string object has a GetHashCode() function. It returns an integer. Convert it into a hex and then to an 8 characters long string. Like so: string hashCode = String.Format(“{0:X}”, sourceString.GetHashCode()); More on that: http://msdn.microsoft.com/en-us/library/system.string.gethashcode.aspx UPDATE: Added the remarks from the link above to this answer: The behavior of GetHashCode is dependent on its implementation, … Read more
If I have a tuple with many elements, is its hash calculated from its elements’ ids or its elements’ content? Neither. It is calculated on the basis of the hashes of these elements, not their “contents” (values/attributes), nor IDs. The basics: why hashes are used the way they are Take a look at this paragraph … Read more
scalar keys %hash or just keys %hash if you’re already in a scalar context, e.g. my $hash_count = keys %hash or print ‘bighash’ if keys %hash > 1000. Incidentally, $#array doesn’t find the number of elements, it finds the last index. scalar @array finds the number of elements.
There is technically a limit, but it’s quite large. The padding scheme used for SHA-256 requires that the size of the input (in bits) be expressed as a 64-bit number. Therefore, the maximum size is (264-1)/8 bytes ~= 2’091’752 terabytes. That renders the limit almost entirely theoretical, not practical. Most people don’t have the storage … Read more
Mainly, because tuples are immutable. Assume the following works: >>> l = [1, 2, 3] >>> t = (1, 2, 3) >>> x = {l: ‘a list’, t: ‘a tuple’} Now, what happens when you do l.append(4)? You’ve modified the key in your dictionary! From afar! If you’re familiar with how hashing algorithms work, this … Read more
Basically you can split your operation into to parts: Somehow “encrypt” your initial number n, so that two consecutive numbers yield (very) different results Construct your “human-readable” code from the result of step 1 For step 1 I’d suggest to use a simple block cipher (e.g. a Feistel cipher with a round function of your … Read more