The Need Definition –
There are some TBs of your Call Data Records(CDR) to be shared with an external company. Some of the columns in this dataset must be encrypted and this encryption method must guarantee that this columns only can be decrypted by you, the company who owns the data.
The Solution Advised –
After 10g we have DBMS_CRYPTO supplied package and inside this package there is the Rijndael(AES) algorithm which was selected by NIST in October 2000 to become the new official Advanced Encryption Standard(AES) for use within the US Government.
AES is available in two strengths; 128 and 256 bits, and of course the 256-bit version is approximately %50 slower than the 128-bit version, so for the optimum encryption performance 128 bit strength will be enough for this need since to break AES128 encryption one will need 2 ^ 100 amount of keys which will mean months of time even with a super-computer.
And why to do this inside the database but not with a custom C program on operating system for example, the answer is simple as usual; you have the PARALLEL QUERY, HASH JOIN, PARTITIONING, COMPRESSION type of VLDB options already available inside the database you paid for so for the other path you will most probably be re-inventing a dumper wheel within more time and this wheel will born with its maintanance costs on long-term.
A Simple Demostration based on the 10g EM Data Encryption Wizard –
Some additional reading and references –