Tweak

Semantic Encryption uses 128 bit key and a Tweak (string upto 16 bytes) in the encryption. Semantic Encryption uses AES 128 bit Symmetric Encryption internally. By modifying Tweak, we can ensure that the encrypted values do not match even when the original values match. 

Example:

Unencrypted Date : 10/12/1992

Date Encrypted by Semantic Encryption (using Tweak = 1234) : 01-25-2036

Date Encrypted by Semantic Encryption (using Tweak = 1235) : 07-16-2020

The above encryption was performed by using the same key. Using different tweak values produced different encrypted dates. When encrypted a date belonging to two different entities (e.g. DOBs for two different persons), different tweak values are recommended. This way the encrypted value will not be same and hence will not reveal the fact that the dates are identical.