You can create an index on an encrypted column, provided that the column’s encryption key does not specify the use of an initialization vector or random padding. Using an initialization vector or random padding results in identical data encrypting to different patterns of ciphertext, which prevents the index from enforcing uniqueness.
Indexes on encrypted data are useful for equality and non-equality matching of data but not for data ordering, range searches, or finding minimum and maximum values. If Adaptive Server is performing an order-dependent search on an encrypted column, it cannot execute an indexed lookup on encrypted data. Instead, the encrypted column in each row must be decrypted and then searched. This process slows the processing of data.
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