If the length of two MD5 hashes are the same does this mean the strength is equal?

Answer 1

MD5 (Message-Digest algorithm 5) is a widely used cryptographic hash function that always has a 128-bit (16 byte) hash value, so all MD5 hashes must be the same length. As far as "strength" is concerned, hashes are intended to provide a means to check whether a message has been tampered with. MD5 digests have been widely used in the software world to provide some assurance that a transferred file has arrived intact. They are NOT a means for encrypting data. For hash functions, "strength" would have to refer to collision resistance - i.e. difficulty of producing another message with different contents but the same hash.

Unfortunately, MD5 is no longer considered to be entirely trustworthy for this purpose; it now that it is easy to generate MD5 collisions (messages with different content but the same hash value). It is possible for the person who created the file to create a second file with the same checksum, so this technique cannot protect against some forms of malicious tampering. Also, in some cases the checksum cannot be trusted (for example, if it was obtained over the same channel as the downloaded file), in which case MD5 can only provide error-checking functionality: it will recognize a corrupt or incomplete download, which becomes more likely when downloading larger files.