Question

For demonstration-purposes, what are a couple examples of strings that collide when hashed? MD5 is a relatively standard hashing-option, so this will be sufficient.

Answer 1

This page provides these examples of 128 byte values hashing to the same value:

d131dd02c5e6eec4693d9a0698aff95c 2fcab58712467eab4004583eb8fb7f89 
55ad340609f4b30283e488832571415a 085125e8f7cdc99fd91dbdf280373c5b 
d8823e3156348f5bae6dacd436c919c6 dd53e2b487da03fd02396306d248cda0 
e99f33420f577ee8ce54b67080a80d1e c69821bcb6a8839396f9652b6ff72a70

and

d131dd02c5e6eec4693d9a0698aff95c 2fcab50712467eab4004583eb8fb7f89 
55ad340609f4b30283e4888325f1415a 085125e8f7cdc99fd91dbd7280373c5b 
d8823e3156348f5bae6dacd436c919c6 dd53e23487da03fd02396306d248cda0 
e99f33420f577ee8ce54b67080280d1e c69821bcb6a8839396f965ab6ff72a70 

Note that although your question asked for “strings” which collide, MD5 is defined over binary data, so the normal text meaning of “string” doesn’t really apply. Languages and libraries which allow you to take the MD5 hash of text data usually mean “encode the string in a specified encoding, then hash the result.”