Does the MD5 algorithm always generate the same output for the same string?

32
votes

Does the MD5 algorithm always generate the same output for the same string?

Is using a salt the only to produce different output?

6
hashmd5
Can you explain why you ask? It seems like you want another behavior for some reason. - Scott Stafford
It is a deterministic algorithm. How could it do otherwise? - President James K. Polk
I am unfamiliar with the differences between cryptography and hashing. I think also had it mixed up RC5 - vfclists

6 Answers

41
votes

Yes, otherwise MD5 would be useless for things like file verification. What reason would you have for non deterministic output?

9
votes

Yes, MD5 always outputs the same given the same input. That's how it's used for passwords. You store the hash in the database, then when the user types their password in, it's hashed again and the two hashes are compared.

NOTE: MD5 is not recommended for hashing passwords because it's cryptographically weak. There are more suitable cryptographic hashes available, such as bcrypt. However, historically, it has been used for this purpose.

8
votes

Yes, a hash algorithm always produces the same output. If you use the same salt, this will also always produce the same output for a given input.

1
votes

Yes MD5 is deterministic, and this is considered a desirable characteristic for many applications of message digest functions.

As for using a salt, by that you really mean 'changing the input string in some subtle way' don't you ? And, of course, it is also a desirable characteristic of message digests that they produce (with very high probability) a different digest for a different message.

0
votes

Yes. MD5 is a hash function.

This does not mean that an MD5 is unique. Multiple inputs could map to the same hash, but any given input has only one hash.

0
votes

Yes. Although in some cases it creates the same hash for different strings.