Calculating storage requirements for encrypted data

EXECUTE FUNCTION LENGTH(ENCRYPT_TDES("1234567890123456", "simple password"));

This returns 55.

EXECUTE FUNCTION LENGTH(ENCRYPT_TDES("1234567890123456", "simple password", 
"12345678901234567890123456789012"));

This returns 107.

EXECUTE FUNCTION LENGTH(ENCRYPT_AES("1234567890123456", "simple password"));

This returns 67.

EXECUTE FUNCTION LENGTH(ENCRYPT_AES("1234567890123456", "simple password", 
"12345678901234567890123456789012"));

This returns 119.

The required storage size for encrypted data is sensitive to three factors:

• N, the number of bytes in the plain text
• whether or not a hint is provided
• which encryption function you use (ENCRYPT_TDES or ENCRYPT_TDES)

The following formulae describe the four possible cases, and are not simplified:

• Encryption by ENCRYPT_TDES( ) with no hint:

  Encrypted size = (4 x ((8 x((N + 8)/8) + 10)/3) + 11)

• Encryption by ENCRYPT_AES( ) with no hint:

  Encrypted size = (4 x ((16 x((N + 16)/16) + 10)/3) + 11)

• Encryption by ENCRYPT_TDES( ) with a hint:

  Encrypted size = (4 x ((8 x((N + 8)/8) + 50)/3) + 11)

• Encryption by ENCRYPT_AES( ) with a hint:

  Encrypted size = (4 x ((16 x((N + 16)/16) + 50)/3) + 11)

The integer division ( / ) returns an integer quotient and discards any remainder.

Based on these formulae, the following table shows the encrypted size (in bytes) for selected ranges of values of N:

N	ENCRYPT_TDES No Hint	ENCRYPT_AES No Hint	ENCRYPT_TDES With Hint	ENCRYPT_AES With Hint
1 to 7	35	43	87	99
8 to 15	43	43	99	99
16 to 23	55	67	107	119
24 to 31	67	67	119	119
32 to 39	75	87	131	139
40 to 47	87	87	139	139
100	163	171	215	227
200	299	299	355	355
500	695	707	747	759