Algorithm to generate unique (possibly auto incremented) ids

Question

I need to generate unique ids for my application and I am looking for suitable algorithms. I would prefer something like this --

YYYY + MM + DD + HH + MM + SS + <random salt> + <something derived from the preceding values>

F.ex. -

20100128184544ewbhk4h3b45fdg544

I was thinking about using SHA-256 or something but the resultant string should not be too long. I could use UUID but again, they are too long and they are guaranteed to be unique on only one machine.

I would welcome suggestions, ideas. My programming language is Java.

Edit: The ids need not be cryptographically secure. I am looking at simpler hashing algos like the one by Dan Bernstein, etc.

Answer 1

Use Microtime....

Answer 2

I think if you use SHA1(MD5(YYYYMMDDHHMMSS + YourSystemName + ClientName)) u'll be fine with 40 chars.. ;)

Answer 3

java.security.messageDigest()?

Answer 4

You could use that SHA-256 and then only take the first 10 bytes from the result (or however many you like, balancing length and uniqueness however you like).

Answer 5

So I have finally settled for this -

d = YYYYMMDDHHMMSS
hash = d + sha256(d + random_salt)[:10]

Thank you all for the response.