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When you use AES or DES symmetric key encryption routines, first define the key that will be used in the encryption operation. Similarly, to decrypt a file specify the same key. Table 11-2 describes the callable routines that maintain keys.
| Routine | Description |
|---|---|
| ENCRYPT$DEFINE_KEY |
Creates a key definition with a key name and a key value. Puts the
definition into a key storage table.
Similar to the ENCRYPT /CREATE_KEY command. |
| ENCRYPT$DELETE_KEY |
Removes a key definition from a key storage table. Uses the key name to
identify the key to be removed.
Similar to the ENCRYPT /REMOVE_KEY command. |
| ENCRYPT$GENERATE_KEY | Generates random key values. |
When you call these routines, use the following arguments:
The ENCRYPT$ENCRYPT_FILE routine is similar to the DCL commands ENCRYPT and DECRYPT in that you use this routine with entire files.
The ENCRYPT$ENCRYPT_FILE routine specifies the key, the input file specification, the output file specification, and other file operation information.
Specify the type of operation, either encryption or decryption, with the file-flags argument for DES and the file-AES argument for AES operations.
ENCRYPT$ENCRYPT_FILE does not require a prior call to ENCRYPT$INIT.
11.6 Operations on Records and Blocks
To operate on small records or blocks of data, use the following routines:
These routines are an abbreviated form of the ENCRYPT$INIT, ENCRYPT$ENCRYPT, ENCRYPT$DECRYPT, ENCRYPT$FINI sequence of calls.
Do not use these routines for data that is larger than a few records.
To use AES for one-record ciphers, an AES key must first be created and
stored in the logical name table (encrypted). The key name of an AES
key is specified as an address of a descriptor that contains the ASCII
text for the selected AESmmmkkk (mode and key size) algorithm;
for example, AESCBC256. Note that the input and output buffers
(descriptor addresses) are also provided.
11.7 Routine Descriptions
This section describes the syntax of each callable routine. The
routines are listed alphabetically.
11.7.1 Specifying Arguments
Each routine's argument list shows the mandatory arguments first, followed by the optional arguments. Brackets ( [ ] ) identify optional arguments in the argument list.
For example, this format line shows that the required arguments are context, input, and output, and that the optional arguments are output-length and p1:
|
ENCRYPT$DECRYPT context ,input ,output [,output-length] [,p1] |
When you specify arguments, follow these guidelines:
Constants are associated with the symbolic names of the bitmasks used by the encryption routines. These constants are defined in the ENCRYPT_STRUCTURES files that are provided with the kit.
The examples directory, ENCRYPT$EXAMPLES, has a copy of the
ENCRYPT_STRUCTURES file in each supported programming language.
11.7.3 Error Handling
By default, encryption signals error conditions with messages. To intercept a message that is inappropriate for your application, supply a condition handler.
For information about implementing condition handlers, see your programming language reference manual.
Decrypts the next record of ciphertext according to the algorithm specified in the ENCRYPT$INIT call.
ENCRYPT$DECRYPT context, input, output [,output-length] [,p1]
context
VMS usage: type: longword integer (signed) access: write only mechanism: by reference
Context area initialized when ENCRYPT$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
VMS usage: type: char_string access: read only mechanism: by descriptor
Ciphertext record that ENCRYPT$DECRYPT is to decrypt. The input argument is the address of a descriptor pointing to a byte-aligned buffer containing the input record to the decryption operation.output
VMS usage: type: char_string access: write only mechanism: by descriptor
Plaintext record that results when ENCRYPT$DECRYPT completes execution. The output argument is the address of a descriptor pointing to a byte-aligned padding buffer that contains the output record from the decryption operation.If the descriptor is dynamic and insufficient space is allocated to contain the output record, storage is 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, for DES, 8 bytes.
output-length
VMS usage: 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$DECRYPT. Retain the byte count of the input data in order to strip trailing pad bytes after a subsequent decryption operation. Note that the AES block-mode algorithms (AESCBCxxx and AESECBxxx), pad the data to even 16-byte block boundaries. For AES, 1 byte encrypts and decrypts to 16 bytes, 72 bytes to 80, and so forth. The AES padding character is a HEX number of bytes indicating the number of bytes padded, for example, the 1-byte encrypted pad decrypts to 15 characters of 0F following the 1 decrypted byte of data. For the 72 bytes of data, 8 bytes of padding characters ( 08 08 ... 08 ) follow the 72 bytes of decrypted data. DESECB and DESCBC modes always pad with characters of zeros. The character stream modes (AESCFBxxx, AESOFBxxx, DESCFB) do not pad the data, so the output-length matches the actual number of data bytes.
p1
VMS usage: type: quadword[1](DES), quadword[2](AES) access: read only mechanism: by reference
Optional argument. The P1 argument is the address of a quadword initialization vector used to seed the two modes of the DES algorithm for which it is applicable (DESECB and DESCFB). (That is, the DES IV initialization vector is a quadword reference, to an 8-byte value.)For AES, the optional P1 argument for the AES IV initialization vector is a reference to a 16-byte (2 quadword) value.
If this argument is omitted, the initialization vector used is the residue of the previous use of the specified context block. ENCRYPT$INIT initializes the context block with an initialization vector of zero.
The ENCRYPT$DECRYPT routine decrypts the next record of ciphertext according to the algorithm specified in the ENCRYPT$INIT call. Any errors encountered in the operation are returned as status values. The message authentication mode (DESMAC) is not supported by ENCRYPT$DECRYPT.The ENCRYPT$DECRYPT routine returns a 32-bit status code indicating the success or failure of the routine's operation.
SS$_NORMAL Record successfully decrypted. ENCRYPT$ xyz An error reported by the encryption software. The xyz portion identifies the message. SS$_ xyz A return status from a called system service. The xyz portion identifies the return status.
Decrypts a small amount of data on a decrypt stream.
Note
To use AES for one-record ciphers, you must first create an AES key, which is stored in the logical name table (encrypted). The key name of an AES key is specified as an address of a descriptor that contains the ASCII text for the selected AESmmmkkk (mode and key size) algorithm, for example, AESCBC256. The input and output buffers (descriptor addresses) are also provided.
ENCRYPT$DECRYPT_ONE_RECORD input, output, key-name, algorithm
input
VMS usage: type: char_string access: read only mechanism: by descriptor
Ciphertext record to be decrypted. The input argument is the address of a string descriptor pointing to a byte-aligned buffer containing the input record to be decrypted.output
VMS usage: type: char_string access: write only mechanism: by descriptor
Plaintext record resulting when ENCRYPT$DECRYPT_ONE_RECORD completes execution. The output argument is the address of a string descriptor pointing to a byte-aligned buffer that contains the plaintext record.If the descriptor is dynamic and insufficient space is allocated to contain the output record, storage is allocated from dynamic memory. If space is insufficient to contain the output of the operation, an error is returned.
The ENCRYPT$DECRYPT_ONE_RECORD routine adjusts the length of the output descriptor, if possible, to reflect the actual length of the output string.
key-name
VMS usage: type: char_string access: read only mechanism: by descriptor
Key used to initialize the decrypt stream. The key-name argument is the address of a string descriptor pointing to the name of the previously defined user key to be used.algorithm
VMS usage: type: char_string access: read only mechanism: by descriptor
Algorithm used for the decryption operation. The algorithm argument is the address of a string descriptor pointing to a code for the selected algorithm. The algorithm code is an ASCII string. Specify the descriptor type value as one of the following:
- DSC$K_DTYPE_T (text)
- DSC$K_DTYPE_VT (varying text)
- DSC$K_DTYPE_Z (unspecified)
For DES, the following algorithms are valid:
- DESCBC (default)
- DESECB
- DESCFB
For AES, the following algorithms are valid:
- Cipher block chaining:
AESCBC128 (default)
AESCBC192
AESCBC256- Electronic code book:
AESECB128
AESECB192
AESECB256- Cipher feedback:
AESCFB128
AESCFB192
AESCFB256- Output feedback:
AESOFB128
AESOFB192
AESOFB256
In some applications, only a small amount of data needs to be decrypted on a particular decrypt stream. The ENCRYPT$DECRYPT_ONE_RECORD routine allows you to perform such a decryption operation.The ENCRYPT$DECRYPT_ONE_RECORD routine is an abbreviated form of the ENCRYPT$INIT, ENCRYPT$DECRYPT, and ENCRYPT$FINI sequence of calls. However, using ENCRYPT$DECRYPT_ONE_RECORD repeatedly to decrypt records of a file is extremely inefficient.
The ENCRYPT$DECRYPT_ONE_RECORD routine returns a 32-bit status code indicating the success or failure of the routine's operation.
SS$_NORMAL Operation performed. ENCRYPT$ xyz An error reported by the Encryption software. The xyz portion identifies the message. SS$_ xyz A return status from a called system service. The xyz portion identifies the return status.
Places a key definition into the process, group, job, or system key storage table.
ENCRYPT$DEFINE_KEY key-name, key-value, key-flags
key-name
VMS usage: type: char_string access: read only mechanism: by descriptor
Name of the key defined when ENCRYPT$DEFINE_KEY completes execution. The key-name argument is the address of a string descriptor pointing to a char_string key that is interpreted as the name of the key to be defined. A maximum of 243 characters is permitted.
Note
Key names beginning with ENCRYPT$ are reserved for HP.key-value
VMS usage: type: char_string access: read only mechanism: by descriptor
Key value defined when ENCRYPT$DEFINE_KEY completes execution. The key-value argument is the address of a string descriptor pointing to a vector of unsigned byte values that are assigned to the named key. A maximum of 240 bytes can be assigned.key-flags
VMS usage: type: longword access: read only mechanism: by reference
Flags that ENCRYPT$DEFINE_KEY uses when defining a key. The key-flags argument is the address of a longword containing flags that control the key definition process.Each flag has a symbolic name. The constants associated with these names are defined in the ENCRYPT$EXAMPLES:ENCRYPT_STRUCTURES files in various programming languages.
Table 11-3 defines the function of each flag.
Table 11-3 ENCRYPT$DEFINE_KEY Flags Flag Symbolic Name Function ENCRYPT$M_KEY_PROCESS Places definition in process table. ENCRYPT$M_KEY_GROUP Places definition in group table. ENCRYPT$M_KEY_JOB Places definition in job table. ENCRYPT$M_KEY_SYSTEM Places definition in system table. ENCRYPT$M_KEY_LITERAL Stores key without compressing. ENCRYPT$M_KEY_AES Designates an AES key value.
The following AES mask can be used in addition to other flags for the key-flags argument (as a longword by reference). An associated AES key value can be used for testing the bit within the program. Use the KEY_AES key flag to specify an AES key:
The ENCRYPT$DEFINE_KEY routine places a key definition into the process, group, job, or system key storage table. The key value supplied with the routine is processed as specified and placed in the key storage table under the indicated name. The ENCRYPT$DEFINE_KEY routine does not interpret the key value.By default, DES keys are treated as char_string keys, using the Digital Multinational Character Set and are compressed before being inserted into the key storage table. The compression proceeds as follows:
- The string is converted to uppercase characters.
- The digits 0 through 9 are left unchanged.
- All characters except letters, numerals, dollar signs, periods, and underscores are converted to spaces.
- All sequences of multiple spaces (or characters that have been converted into spaces) are converted into single spaces.
When a char_string key is retrieved from key storage for use as a DES key, it is folded into an 8-byte key by exclusive OR-ing of 8-byte segments of the key string together, and then by applying odd parity to each byte by modifying the sign bit (bit 7).
The key flag ENCRYPT$M_KEY_LITERAL specifies that the key string supplied is a binary key. A binary key is not compressed, but is placed into key storage as is. When a binary key is used as a DES key, it is likewise folded into an 8-byte key by exclusive OR-ing of 8-byte segments together. For DES, odd parity is then applied by modifying the low bit (bit 0) of each byte.
AES key values are not subject to ASCII compression. Therefore, any 8-bit character is allowed for AES keys.
The ENCRYPT$DEFINE_KEY routine returns a 32-bit status code indicating the success or failure of the routine's operation.
SS$_NORMAL Key has been defined. ENCRYPT$ xyz An error reported by the Encryption software. The xyz portion identifies the message. SS$_ xyz A return status from a called system service. The xyz portion identifies the return status.
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