Decrypt Data (QC3DECDT, Qc3DecryptData) API


  Required Parameter Group:

1 Encrypted data Input Char(*)
2 Length of encrypted data Input Binary(4)
3 Algorithm description Input Char(*)
4 Algorithm description format name Input Char(8)
5 Key description Input Char(*)
6 Key description format name Input Char(8)
7 Cryptographic service provider Input Char(1)
8 Cryptographic device name Input Char(10)
9 Clear data Output Char(*)
10 Length of area provided for clear data Input Binary(4)
11 Length of clear data returned Output Binary(4)
12 Error code I/O Char(*)

  Service Program Name: QC3DTADE

  Default Public Authority: *USE

  Threadsafe: Yes

The Decrypt Data (OPM, QC3DECDT; ILE, Qc3DecryptData) API restores encrypted data to a clear (intelligible) form.

Information on cryptographic standards can be found in Create Algorithm Context (OPM, QC3CRTAX; ILE, Qc3CreateAlgorithmContext) API.


Authorities and Locks

Required device description authority
*USE

Required file authority
*OBJOPR, *READ

Required Parameter Group

Encrypted data
INPUT; CHAR(*)

The data to decrypt.

Length of encrypted data
INPUT; BINARY(4)

The length of the encrypted data parameter.
If the mode of operation is CFB 1-bit, this length must be specified in bits.

Algorithm description
INPUT; CHAR(*)

The algorithm and associated parameters for decrypting the data.
The format of the algorithm description is specified in the algorithm description format name parameter.

Algorithm description format name
INPUT; CHAR(8)

The format of the algorithm description. The possible format names follow.

ALGD0100
The token for an algorithm context. This format must be used when performing the decrypt operation over multiple calls. After the last call (when the final operation flag is on), the context will reset to its initial state and can be used in another API.

ALGD0200
Parameters for a block cipher algorithm (DES, Triple DES, AES, and RC2).

ALGD0300
Parameters for a stream cipher algorithm (RC4-compatible).

ALGD0400
Parameters for a public key algorithm (RSA).

See Algorithm Description Formats for a description of these formats.

Key description
INPUT; CHAR(*)

The key and associated parameters for decrypting the data.
The format of the key description is specified in the key description format name parameter.

If the decrypt operation extends over multiple calls (see ALGD0100 description above), only the key description from the first call will be used. Therefore, on subsequent calls, you may set the pointer to this parameter to NULL.

Key description format name
INPUT; CHAR(8)

The format of the key description.
If the pointer to the key description parameter is NULL, this parameter will be ignored. The possible format names follow.

KEYD0100
Key context token. This format identifies a key context. A key context is used to store a key value so it need not be recreated or retrieved every time it is used. To create a key context, use the Create Key Context (OPM, QC3CRTKX; ILE, Qc3CreateKeyContext) API.

KEYD0200
Key parameters.

KEYD0400
Keystore label. This format identifies a key from keystore. For more information about cryptographic services keystore, see Cryptographic Services Keystore.

KEYD0500
PKCS5 passphrase. This format derives a key using RSA Data Security, Inc. Public-Key Cryptography Standard (PKCS) #5.

KEYD0600
PEM certificate. This format uses the PKA key in an ASCII encoded PEM based certificate.

KEYD0700
Certificate label. This format uses the public PKA key identified by a label into system certificate keystore (*SYSTEM).

KEYD0800
Distinguished name. This format uses the public PKA key identified by a distinguished name for a certificate in system certificate keystore (*SYSTEM).

KEYD0900
Application identifier. This format uses the private PKA key identified by an application identifier. The application identifier must be assigned to a valid certificate label in system certificate keystore (*SYSTEM).

See Key Description Formats for a description of these formats.

Cryptographic service provider
INPUT; CHAR(1)

The cryptographic service provider (CSP) that will perform the decryption operation.

0 Any CSP.
The system will choose an appropriate CSP to perform the decryption operation.
1 Software CSP.
The system will perform the decryption operation using software. If the requested algorithm is not available in software, an error is returned.
2 Hardware CSP.
The system will perform the decryption operation using cryptographic hardware. If the requested algorithm is not available in hardware, an error is returned. A specific cryptographic device can be specified using the cryptographic device name parameter. If the cryptographic device is not specified, the system will choose an appropriate one.

Cryptographic device name
INPUT; CHAR(10)

The name of a cryptographic device description.
This parameter is valid when the cryptographic service provider parameter specifies 2 (hardware CSP). Otherwise, this parameter must be blanks or the pointer to this parameter set to NULL.

Clear data
OUTPUT; CHAR(*)

The area to store the decrypted data.

Length of area provided for clear data
INPUT; BINARY(4)

The length of the clear data parameter.
If the mode of operation is CFB 1-bit, this length must be specified in bits.
To ensure sufficient space, specify an area at least as large as the length of encrypted data. If the length of area provided for clear data is too small, an error will be generated and no data will be returned in the clear data parameter.

Length of clear data returned
OUTPUT; BINARY(4)

The length of the clear data returned in the clear data parameter.
If the mode of operation is CFB 1-bit, this length will be returned in bits.

Error code
I/O; CHAR(*)

The structure in which to return error information.
For the format of the structure, see Error code parameter.



Algorithm Description Formats

For detailed descriptions of the table fields, see Algorithm Description Formats Field Descriptions.

ALGD0100 Format

Offset Type Field
Dec Hex
0 0 CHAR(8) Algorithm context token
8 8 CHAR(1) Final operation flag

ALGD0200 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Block cipher algorithm
4 4 BINARY(4) Block length
8 8 CHAR(1) Mode
9 9 CHAR(1) Pad option
10 A CHAR(1) Pad character
11 B CHAR(1) Reserved
12 C BINARY(4) MAC length
16 10 BINARY(4) Effective key size
20 14 CHAR(32) Initialization vector or counter

ALGD0300 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Stream cipher algorithm

ALGD0400 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Public key cipher algorithm
4 4 CHAR(1) PKA block format
5 5 CHAR(3) Reserved
8 8 BINARY(4) Signing hash algorithm


Algorithm Description Formats Field Descriptions

Algorithm context token
A token for an algorithm context. The algorithm context is created by using the Create Algorithm Context (OPM, QC3CRTAX; ILE, Qc3CreateAlgorithmContext) API.

Block cipher algorithm
The decryption algorithm. Following are the valid block cipher algorithms.
20 DES
21 Triple DES
22 AES
23 RC2

Block length
The algorithm block length. For DES, Triple DES, and RC2, the block length field must specify 8. The valid block length values for AES are 16, 24, and 32.

Effective key size
For RC2, the number of key bits to use in the cipher operation. Valid values are from 1 to 1024. If RC2 is not specifed for the block cipher algorithm, this field must be set to 0.

Final operation flag
The final processing indicator.
0 Continue.
The system will not perform final processing and the algorithm context will maintain the state of the operation. The algorithm context can be used on future calls to this API to continue the decryption operation.
1 Final.
The system will perform final processing (e.g. remove padding) and the algorithm context will reset to its initial state. The algorithm context can then be used to begin a new cryptographic operation (encrypt, decrypt, etc.). When performing a final operation, the pointer to the encrypted data parameter may be set to NULL and the length of encrypted data parameter set to 0. Final must be specified when performing an RSA operation.

Initialization vector or counter
An initialization vector (IV) is used for modes CBC, OFB, CFB, and CUSP. A counter is used for CTR mode. Refer to the mode standards for an explanation of how each mode uses the IV or counter. This field is not used for ECB mode, and must be set to NULL (binary 0s).
For DES, Triple DES, and RC2, the first 8 bytes are used as the IV/counter. For AES, the length of the IV/counter is that specified by block length.
The IV/counter must be the same as the IV/counter used to encrypt the data.

MAC length
This field is not used on a decrypt operation and must be set to null (binary 0s).

Mode
The mode of operation. Information on modes can be found in FIPS PUB 81 and ANSI X9.52. Following are the valid modes.
0 ECB.
1 CBC.
2 OFB. Not valid with AES or RC2.
3 CFB 1-bit. Not valid with AES or RC2.
4 CFB 8-bit. Not valid with AES or RC2.
5 CFB 64-bit. Not valid with AES or RC2.
6 CUSP. CUSP is a special type of CBC mode documeted in the z/OS® ICSF Application Programmer's Guide (SA22-7522). It is used for handling data not a multiple of the block length. The length of encrypted data in CUSP mode will always equal the length of clear text data.
7 CTR. Only valid with AES.

Pad character
This field is not used on a decrypt operation and must be set to null (binary 0s).

Pad option
If requested, padding is removed at the end of the decrypt operation. Padding is not performed for modes CFB 1-bit, CFB 8-bit, and CUSP. In these cases, the pad option must be set to 0. Do not specify remove padding if the data was not padded when encrypted. Following are the valid pad options.
0 Do not remove padding.
1 Remove padding.

PKA block format
The public key algorithm block format. Following are the valid values.
0 PKCS #1 block type 00
1 PKCS #1 block type 01
2 PKCS #1 block type 02
This format is recommended when decrypting non-hash items (such as keys). The other formats are normally used in sign and verify functions.
4 Zero pad
Zero pad is not removed.
6 OAEP

Public key cipher algorithm
The decryption algorithm. Following are the valid public key cipher algorithms.
50 RSA

Reserved
Must be null (binary 0s).

Signing hash algorithm
This field is not used on a decrypt operation and must be set to null (binary 0s).

Stream cipher algorithm
The decryption algorithm. Following are the valid stream cipher algorithms.
30 RC4-compatible


Key Description Formats

For detailed descriptions of the table fields, see Key Description Formats Field Descriptions.

KEYD0100 Format

Offset Type Field
Dec Hex
0 0 CHAR(8) Key context token

KEYD0200 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Key type
4 4 BINARY(4) Key string length
8 8 CHAR(1) Key format
9 9 CHAR(3) Reserved
12 C CHAR(*) Key string

KEYD0400 Format

Offset Type Field
Dec Hex
0 0 CHAR(20) Qualified keystore file name
20 14 CHAR(32) Record label
52 34 CHAR(4) Reserved

KEYD0500 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Key type
4 4 BINARY(4) Derived key length
8 8 BINARY(4) Iteration count
12 C BINARY(4) Salt length
16 10 CHAR(16) Salt
32 20 BINARY(4) Passphrase CCSID
36 24 BINARY(4) Passphrase length
40 28 CHAR(*) Passphrase

KEYD0600 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) PEM certificate length
4 4 CHAR(4) Reserved
8 8 CHAR(*) PEM certificate

KEYD0700 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Certificate label length
4 4 CHAR(4) Reserved
8 8 CHAR(*) Certificate label

KEYD0800 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Distinguished name length
4 4 CHAR(4) Reserved
8 8 CHAR(*) Distinguished name

KEYD0900 Format

Offset Type Field
Dec Hex
0 0 BINARY(4) Application identifier length
4 4 CHAR(4) Reserved
8 8 CHAR(*) Application identifier


Key Description Formats Field Descriptions

Application identifer
The application ID assigned to a certificate with a private key in system certificate keystore (*SYSTEM).

Application identifier length
The length of the application ID. The length can not be greater than 32.

Certificate label
The label of the certificate in system certificate keystore (*SYSTEM). The certificate's public key will be used in the decryption operation.

Certificate label length
The length of the certificate label.

Derived key length
The length of key requested. The minimum allowed length is 1.

Distinguished name
The distinguished name of the certificate in system certificate keystore (*SYSTEM). The certificate's public key will be used in the decryption operation.

Distinguished name length
The length of the distinguished name.

Iteration count
Used to greatly increase the cost of an exhaustive search while modestly increasing the cost of key derivation. The minimum allowed value is 1. The standard recommends a minimum of 1000. The maximum allowed length is 100,000.

Key context token
A token for a key context. The key context is created by using the Create Key Context (OPM, QC3CRTKX; ILE, Qc3CreateKeyContext) API.

Key format
The format of the key string field. Following are the valid values.
0 Binary string.
The key is specified as a binary value.
1 BER string
If the key type field specifies 50 (RSA public), the key must be specified in BER encoded X.509 Certificate or SubjectPublicKeyInfo format. For specifications of this format, refer to RFC 3280. If the key type field specifies 51 (RSA private), the key must be specified in BER encoded PKCS #8 format. For specifications of this format, refer to RSA Security Inc. Public-Key Cryptography Standards. To generate a PKA key pair, use the Generate PKA Key Pair (OPM, QC3GENPK; ILE, Qc3GenPKAKeyPair) API.

Key string
The key to use in the decrypt operation.

Key string length
Length of the key string specified in the key string field.

Key type
The type of key. Following are the valid values.
20 DES
The key string length or derived key string length must be 8 bytes. For key description KEYD0200, the key format must be 0. Only 7 bits of each byte are used as the actual key. The rightmost bit of each byte is used to set parity. Some cryptographic service providers require that a DES key have odd parity in every byte. Others ignore parity.
21 Triple DES
The key string length or the derived key length can be 8, 16, or 24. For key description KEYD0200, the key format must be 0. Triple DES operates on a decryption block by doing a DES decrypt, followed by a DES encrypt, and then another DES decrypt. Therefore, it actually uses three 8-byte DES keys. If 24 bytes are supplied in the key string, the first 8 bytes are used for key 1, the second 8 bytes for key 2, and the third 8 bytes for key 3. If 16 bytes are supplied, the first 8 bytes are used for key 1 and key 3, and the second 8 bytes for key 2. If only 8 bytes are supplied, it will be used for all 3 keys (essentially making the operation equivalent to a single DES operation). Only 7 bits of each byte are used as the actual key. The rightmost bit of each byte is used to set parity. Some cryptographic service providers require that a Triple DES key have odd parity in every byte. Others ignore parity.
22 AES
The key string length or derived key length can be 16, 24, or 32. For key description KEYD0200, the key format must be 0.
23 RC2
The key string length or derived key length can be from 1 to 128. For key description KEYD0200, the key format must be 0.
30 RC4-compatible
The key string length or derived key length can be from 1 to 256. For key description KEYD0200, the key format must be 0.
50 RSA public
Valid only for key description KEYD0200. The key format must be 1. Use an RSA public key if the data was encrypted with an RSA private key. Encryption with a private key and decryption with a public key is used for data authentication (e.g. sign/verify).
51 RSA private
Valid only for key description KEYD0200. The key format must be 1. Use an RSA private key if the data was encrypted with an RSA public key. Encryption with a public key and decryption with a private key is used for data privacy.
Passphrase
A text string.

Passphrase CCSID
INPUT; BINARY(4)

The CCSID of the passphrase. The passphrase will be converted from the specified CCSID to Unicode before calling the PKCS5 algorithm.

0 The CCSID of the job is used to determine the CCSID of the data to be converted. If the job CCSID is 65535, the CCSID from the default CCSID (DFTCCSID) job attribute is used.
1-65533 A valid CCSID in this range is used. For a list of valid CCSIDs, see the i5/OS globalization topic collection.

Passphrase length
The length of passphrase. The length must be in the range of 1 to 256.

PEM certificate
An ASCII encoded PEM formated certificate.

PEM certificate length
The length of the PEM certificate.

Qualified keystore file name
The keystore file where the key is stored. Keystore files are created by using the Create Keystore (OPM, QC3CRTKS; ILE, Qc3CreateKeyStore) API. The first 10 characters contain the file name. The second 10 characters contain the name of the library where the keystore file is located. You can use the following special values for the library name.
*CURLIB The job's current library is used to locate the keystore file. If no library is specified as the current library for the job, the QGPL library is used.
*LIBL The job's library list is searched for the first occurence of the specified file name.

Record label
The label of a key record in a keystore file. The label will be converted from the job CCSID, or if 65535, the job default CCSID (DFTCCSID) job attribute to CCSID 1200 (Unicode UTF-16). Key records are created by using the Write Key Record (OPM, QC3WRTKR; ILE, Qc3WriteKeyRecord) API or the Generate Key Record (OPM, QC3GENKR; ILE, Qc3GenKeyRecord) API.
Reserved
Must be null (binary 0s).

Salt
Used to help thwart attacks by producing a large set of keys for each passphrase. The standard recommends the salt be generated at random and be at least 8 bytes long. You may use the Generate Pseudorandom Numbers (OPM, QC3GENPRN; ILE, Qc3GenPRNs) API to obtain a random value. Additionally, data that distinguishes between various operations can be added to the salt for additional security. Refer to the standard for more information.

Salt length
The length of salt. The length must be in the range of 1 to 16.

Error Messages

Message ID Error Message Text
CPF24B4 E Severe error while addressing parameter list.
CPF3C1E E Required parameter &1 omitted.
CPF3CF1 E Error code parameter not valid.
CPF3CF2 E Error(s) occurred during running of &1 API.
CPF9872 E Program or service program &1 in library &2 ended. Reason code &3.
CPF9D86 E Decryption with PKA private key failed.
CPF9D94 E A pending value exists for a master key.
CPF9D99 E Error openning certificate store.
CPF9D9A E Key is protected by a cryptographic coprocessor.
CPF9D9B E Internal error occured retrieving key from system certificate store.
CPF9D9C E Function is disallowed with specified key context.
CPF9D9F E Not authorized to keystore file.
CPF9DA0 E Error occured opening keystore file.
CPF9DA1 E Key record not found.
CPF9DA2 E Option 34 is not installed.
CPF9DA3 E Not authorized to use APPIDs.
CPF9DA4 E APPID is not valid.
CPF9DA5 E Keystore file not found.
CPF9DA6 E The keystore file is not available.
CPF9DA7 E File is corrupt or not a valid keystore file.
CPF9DA8 D The application identifier length is not valid.
CPF9DA9 D The format of the PEM certificate is not valid.
CPF9DAA D A key requires translation.
CPF9DAB E A key can not be decrypted.
CPF9DB1 E The CCSID is not valid.
CPF9DB3 E Qualified keystore file name not valid.
CPF9DB6 E Record label not valid.
CPF9DB8 E Error occured retrieving key record from keystore.
CPF9DBA E Derived key length not valid.
CPF9DBB E Iteration count not valid.
CPF9DBC E Salt length not valid.
CPF9DBD E Passphrase length not valid.
CPF9DBE E PEM certificate length not valid.
CPF9DBF E Certificate label length not valid.
CPF9DC0 E Distinghished name length not valid.
CPF9DC2 E Key-encrypting algorithm context not compatible with key-encrypting key context.
CPF9DC3 E Unable to decrypt data or key.
CPF9DC6 E Algorithm not valid for encrypting or decrypting a key.
CPF9DC8 E The input data parameter specifies a NULL pointer.
CPF9DD2 E Algorithm description format name not valid.
CPF9DD3 E Key description format name not valid.
CPF9DD5 E Length of input data not valid.
CPF9DD6 E Length of area provided for output data is too small.
CPF9DD7 E The key-encrypting key context for the specified key is not valid or was previously destroyed.
CPF9DD8 E The key-encrypting algorithm context for the specified key is not valid or was previously destroyed.
CPF9DD9 E Effective key size not valid.
CPF9DDA E Unexpected return code &1.
CPF9DDB E The key string or Diffie-Hellman parameter string is not valid.
CPF9DDD E The key string length is not valid.
CPF9DDE E Cipher algorithm not valid.
CPF9DDF E Block length not valid.
CPF9DE0 E Hash algorithm not valid.
CPF9DE1 E Initialization vector or counter not valid.
CPF9DE2 E MAC (message authentication code) length not valid.
CPF9DE3 E Mode not valid.
CPF9DE4 E Pad option not valid.
CPF9DE5 E PKA (public key algorithm) block format not valid.
CPF9DE6 E Public key algorithm not valid.
CPF9DE7 E Key type not valid.
CPF9DE9 E Key format not valid.
CPF9DEC E Cryptographic service provider not valid.
CPF9DED E Final operation flag not valid.
CPF9DEE E Reserved field not null.
CPF9DF0 E Operation, algorithm, or mode not available on the requested CSP (cryptographic service provider).
CPF9DF1 E The algorithm context token does not reference a valid algorithm context.
CPF9DF2 E The algorithm context is not found or was previously destroyed.
CPF9DF3 E Algorithm in algorithm context not valid for requested operation.
CPF9DF4 E The key context token does not reference a valid key context.
CPF9DF5 E The key context is not found or was previously destroyed.
CPF9DF7 E Algorithm context not compatible with key context.
CPF9DF8 E Cryptographic device name not valid.
CPF9DF9 E Cryptographic device not found.
CPF9DFB E Cryptographic service provider (CSP) conflicts with the key context CSP.
CPF9DFD E Not authorized to device.
CPF9DFE E Cryptographic device not available.

API introduced: V5R3

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