Hashing function with partially-reversable part

Is there any known hashing algorithm, which for similar input returns similar output? I need it for creating 'tickets' without checking them against DB. My idea is that I create token carrying (userID and timestamp) (not reversable), and pass this tok开发者_高级运维en along with userID, and be able to check, if the token has given UserID, and, for example, was created 10 minutes ago -

for example, change on first 4 bytes gives significantly different tokens, but with change on last 4 bytes the hashing function returns similar tokens.

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Hm. I'd probably try HMACs: generate a secret key only known to your application. Whenever you need to hand out a new "ticket",

• concatenate user ID and timestamp (say, using serialized representations)
• create a HMAC digest of the above , using the "secret key" as the signing key

Then hand out the triple (user ID, timestamp, digest) to other parties. In order to veriy such a ticket, just do the same:

• extract the user ID and timestamp from the triple.
• generate the HMAC just like above from this information

The generated digests have to match, otherwise someone did try to present you a tampered ticket. This is secure, since only your application knows the secret key, and thus, can generate a suitable HMAC digest. Since the timestamp information comes back plain to you, you can make all required tests with respect to some timing window or whatever.