When i try to encrypt a string using encryption library by CI, the returned string is very big,around 178 chars long. Is there is any method to reduce the length of the string. default cipher is: AES-128.
Suppose: $data=$this->encryption->encrypt("welcome to ooty");
it returns 178 length string value.. i need it to be reduced under 20
Update: When I encrypt a number, say 6 , it returns 178 long string.
Encryption does not reduce the data length.
AES encryption output length depends on the mode. A streaming mode such as CTR mode will not change the length. A block mode such as ECB or CBC will need to be padded to a multiple of block length but PKCS#7 padding will only increase the length a maximum of one block size, 16-bytes for AES.
There is more going on than just encrypting the bytes. A mode such as CBC may be used and the IV (one block length) may be prepended to the encrypted data. Authentication may be added and that could add perhaps 32-bytes. There may be password derivation and the salt and count may be added. Finally the result may be encoded to Base64 or hexadecimal which would increase the length respectively 33% or 100%.
Potential case: "welcome to ooty" is 15 bytes. padding is 1 byte, authentication 32-bytes, salt 32-bytes, count 2-bytes, version 1-byte = 83-bytes, hex encoded = 166-bytes, close to the 178 bytes you are getting.
All this extra buys security. Depending on you use it may not all be necessary, consult a cryptographic domain expert.