context
type: longword integer (signed)
access: write only
mechanism: by reference
Context area initialized when ENCRYPT$INIT completes execution.
The context argument is the address of a longword of unspecified
interpretation that is used to convey context between encryption
operations.
input
type: char_string
access: read only
mechanism: by descriptor
Ciphertext record that ENCRYPT$DECRYPT is to decrypt. The input
argument is the address of a descriptor pointing to a byte-
aligned buffer containing the input record to the decryption
operation.
output
type: char_string
access: write only
mechanism: by descriptor
Plaintext record that results when ENCRYPT$DECRYPT completes
execution. The output argument is the address of a descriptor
pointing to a byte-aligned padding buffer that will contain the
output record from the decryption operation.
If the descriptor is dynamic and insufficient space is allocated
to contain the output record, storage will be allocated from
dynamic memory. If insufficient space exists to contain the
output of the operation, then an error status is returned.
The ENCRYPT$DECRYPT routine adjusts the length of the output
descriptor, if possible, to reflect the actual length of the
output string. If the descriptor type is not DSC$K_DTYPE_VS
(varying string), DSC$K_DTYPE_V (varying), or DSC$K_DTYPE_D
(dynamic), the routine takes the actual output count from the
output-length argument.
The output buffer must be able to accommodate a padded block to
an increment of the block length. For AES this is 16 bytes and
for DES, eight bytes.
output-length
type: word integer
access: write only
mechanism: by reference
Optional argument.
Number of bytes that ENCRYPT$DECRYPT wrote to the output buffer.
The output-length argument is the address of a word containing
the number of bytes written to the output buffer, including any
bytes of pad characters generated by the selected algorithm to
meet length requirements of the input buffer, if any. Output
length does not count padding in the case of a fixed-length
string.
Some encryption algorithms have specific requirements for the
length of the input and output strings. In particular, DESECB
and DESCBC pad input data with from 1 to 7 bytes to form complete
64-bit blocks for operation. The values of the pad characters are
indeterminate.
When you decrypt fewer than 8 bytes, present the full 8 bytes
resulting from the ENCRYPT$ENCRYPT to ENCRYPT$DECRYPT. Retain the
byte count of the input data in order to strip trailing pad bytes
after a subsequent decryption operation. Note that the AES block
mode algorithms (AESCBCxxx and AESECBxxx), pad the data to even
16 byte block boundaries. For AES, one byte encrypts and decrypts
to 16 bytes, 72 bytes to 80, and so forth. The AES padding
character is a HEX number of bytes indicating the number of bytes
padded, for example, the one byte encrypted pad would decrypt to
15 characters of 0F following the one decrypted byte of data. For
the 72 bytes of data, eight bytes of padding characters (08 08
... 08), would follow the 72 bytes of decrypted data. DESECB and
DESCBC modes always pad with characters of zeros. The character
stream modes (AESCFBxxx, AESOFBxxx, DESCFB), do not pad the data,
so the output-length will match the actual number of data bytes.
p1
type: quadword[1](DES), quadword[2](AES)
access: read only
mechanism: by reference
Optional argument. The p1 argument is the address of a quadword
initialization vector used to seed the two modes of the DES
algorithm for which it is applicable (DESECB and DESCFB). (That
is, the DES IV initialization vector is a quadword reference, to
an eight byte value.)
For AES, the optional P1 argument for the AES IV initialization
vector is a reference to a 16 byte (two quadwords) value.
If this argument is omitted, the initialization vector used is
the residue of the previous use of the specified context block.
ENCRYPT$INIT initializes the context block with an initialization
vector of zero.