As part of my scenario of encrypting a file and sending the encrypted file to another z/OS system, I struggled to understand why the documentation referred to transportation keys, key encryption keys (KEKs), import keys and export keys.

I found the subject very unclear. As I currently see it (and I’ve changed my view several times). You need the matching key on each system. If this is a symmetric key, it is the same key. If you are using PKI, they keys are asymmetric.

How do you get symmetric keys on both systems. I see there are two ways

1. Generate the same key on both systems This can be done using private and public keys, and a technique called Diffie-Hellman.
2. Generate a key on one system, and send it securely to the other system. For this you need to securely package the symmetric keys while they are in transit.

I was able to perform the setup and transfer a file securely to another system without the need for these additional keys. What was I missing?

The discussion about transport keys is for the second example where keys are sent over the network. You can use a CIPHER key to encrypt the key. It comes down to can I do it ? Yes. Should I do it ? No (well, maybe not, it depends on the scale of risk).

Within an IT environment the userid administration should be a different team to the systems programmers. This is to prevent any conflict of interest, fraud, and errors. The system programmers cannot give themselves access to sensitive data. In my small company (with just me in it) I have to do sysprog and userid administration.

IBM has similar guidelines for implementing cryptography. For example

• Separation of the roles and responsibilities. The people who create keys are different from the people who give access to the keys, and from the people who use the keys.
• Separation of encryption keys based on what they are used for. A key for encrypting datasets should not be used for encrypting a key to send to a remote system. If a data set encryption key is made public, the key-encryption-key should still be secure.

I could provide isolation of keys by having two keys, one is authorised only for data set encryption and the other authorised only for key encryption, but this separation may not be enough.

Creating exporter/importer using the API

I spent a couple of days trying to create an importer/exporter pair. I found one way of doing it – there may be other (more obscure) ways. It uses Diff-Hellman to create the same key on two sites without transferring sensitive material. I describe it here. It requires each side to have its own private key, and the public key of the other side.

There are three parts

• Generate a skeleton
• Use the skeleton, private key and public key to generate the Diffi-Hellman key
• store it in the key store

Exporter:Generate a skeleton

I used CSNBKTB2 with rules ‘AES ‘||’INTERNAL’||’EXPORTER’.

Exporter:Generate the DH Key

I have a “helper” rexx function which has parameters, private key name, public key name, the completed skeleton.

It used CSNDEDH with

• rule_array = ‘DERIV01 ‘||’KEY-AES ‘
• party_identifier (a string both sides agree) = ‘COLINS-id’
• KEK_key_identifier_length = 0. This is used when the private key is not stored in the PKDS, but passed in encrypted. I think of this as acting as a proxy. “Here is the private key to use – but it has been encrypted with the KEK which is in your local key store”. Setting the length to zero says the private key>is< in the local key store. Definitely an advanced topic!
• Name of side A’s private key in the PKDS
• Name of side B’s public key (from the other side) in the PKDS
• key_bit_length = 256.

It returns a blob encrypted with the local master key.

Exporter:addckds

This is another rexx helper. It takes the name of the key to generate, the encrypted blob, and “replace=Y|N”

This uses

• CSNBKRC2 to add to the CKDS
• if it gets record found, and needs to delete it,
  • it invokes delckds which uses CSNBKRD to delete it
  • it tries the add again

Importer ( on the remote system)

The steps are the same, except

• I used CSNBKTB2 with rules ‘AES ‘||’INTERNAL’||’IMPORTER’.
• Generate the DH key, you use the other keys, side B’s private, and side A’s public.

To export a key using exporter/importer

If you are using an AES exporter key to encrypt the data you need to use CSNDSYX with

• The name of the key you want to export
• The label of the AES exporter key
• rule_array = ‘AES ‘||’AESKW ‘

It returns a blob which you can write to a data set.

To import the key using exporter/importer

read the data into a buffer

Use CSNDSYI2 with

• rule_array = ‘AES ‘||’AESKW ‘
• the name of the importer key

It returns a blob of data.

Use the helper addckds passing the new label name, the blob of data, and replace=yes|no.

• This uses CSNBKRC2 to add the record, with rule_array = ”
• If the record exists and replace=yes then
  • use delckds with CSNBKRD and rule_array = ‘LABEL-DL’
  • re-add it

To export a key using PKI public/private keys

If you are using an PKI cipher key to encrypt the data you need to use CSNDSYX with

• The name of the key you want to export
• The label of the PKI public key
• rule_array = ‘AES ‘||’PKOAEP2 ‘

To import the key using pki private key

read the data into a buffer

Use CSNDSYI2 with

• rule_array = ‘AES ‘||’PKOAEP2 ‘, matching the exporter
• the name of the private key

It returns a blob of data.

Use the helper addckds passing the new label name, the blob of data, and replace=yes|no.

• This uses CSNBKRC2 to add the record, with rule_array = ”
• If the record exists and replace=yes then
  • use delckds with CSNBKRD and rule_array = ‘LABEL-DL’
  • re-add it

ICSF provides APIs and commands to manage cryptographic keys. For example to encrypt a datasets you need to define the key that will be used.

You can use Rexx to use the API’s and make your own commands.

There are some Rexx samples provided with ICSF, and there are others on the internet if you search for the API function and Rexx. These tend to be a large Rexx exec written to do one function.

You can use the power of Rexx to allow significant reuses of these execs, by having one Rexx exec to generate a key, another Rexx exec to add it to the keystore, another Rexx exec to export it, and another Rexx exec to import it.

Background

Rexx Address linkpgm facility

With TSO Rexx there is the “address linkpgm” command environment. This allows you to call z/OS functions with Rexx parameters.

For example

rc = 0
y=”Mystring”
z= 16
address linkpgm “ZOSPROG myrc Y Z”

generates the standard low level request

call ZOSPROG(addr(myrc),addr(y),addr(z));

It returns a variable ‘RC’ for example -3 if the program is not found, or the return code from the program.

Be careful not to specify ‘RC’ as a parameter as it may override it.

If does what you tell it. If you are expecting a string to be returned, then the variable you give it must be big enough to hold the data, it cannot allocate a bigger string.

If you want to create a variable of a fixed size you can use

token         = copies(’00’x,3500);

If you are passing a number or hex string, you have to convert it to the internal value.

For example on input

myInt = ‘00000000’x
mylen = C2D(length(“ABCDEFG”),4) /* the 4 says make field 4 (int) wide */

on output, convert the hex return code to a readable hex code

myrc = c2x(myrc)

To create an internal format length you can use either of

lToken = ‘00001964’x /* 6500 */
lToken = d2c(6500,4); /* of size 4*/

Passing parameters to external Rexx programs

You can call external Rexx programs and get a returned data. For example

with the program mycode

parse arg a,b
return 0 “COLINS”||A b||”xxx”

and call it using

zz = mycode(“AA”,”B”)
say zz
parse var zz rc x y
say rc
say x
say y

gives

0 COLINSAA Bxxx
0
COLINSAA
Bxxx

Using this you can have an external function which generates an AES key, which returns the return code, reason code and the data.

Using hex strings

Many of the ICSF functions return a hex structure. You can convert this from internal using the Rexx function c2x. This takes a string and creates the hex version of it. When you want to use it in another ICSF function you convert it back again using x2c().

x = ‘ABC’
y = c2x(x)
say ‘y:’y /* gives y:C1C2C3 */

When an ICSF function returns data, you can convert it to the hex string, and return it to the caller.

Using lengths

If a hex length has been returned, you can convert it to a Rexx number using C2D

x = ‘00000000c’x
say ‘x:’c2d(x) /* prints x:12 */

Converting from Rexx to internal format

x = 14
y = d2c(x,4) /* a 4 byte field */
say ‘x:’c2x(y) /* display in hex gives x:0000000E */

Using ICSF from Rexx

Using the program

/*********************************************/ 
/* Generate a 256-bit AES DATA key to export */ 
/*********************************************/ 
rc = genAES() /* this returns several bits of data*/
say "CPBKGN " rc 

parse var rc myrc myrs key 
if myrc <> 0 then return rc 
                                                                         
/********************************************/ 
/* Store the AES DATA key in the CKDS       */ 
/********************************************/ 
/* just return code */ 
rc= addCKDS("REXXLABEL",key) 
say "CPBkrc2" rc 
return 0 

And GENAES

say "In GenAES" 
parse arg a  /* no parameters passed in */ 
/********************************************/ 
/* Generate a 256-bit AES DATA key to export*/ 
/********************************************/ 
key_form               = 'OP  ' 
key_length             = 'KEYLN32 ' 
key_type_1             = 'AESDATA ' 
key_type_2             = '' 
kek_id_1               = COPIES('00'x,64) 
kek_id_2               = '' 
generated_key_id_1 = COPIES('00'x,64) 
generated_key_id_2 = '' 
                                                                   
myrc             = 'FFFFFFFF'x 
myrs              = 'FFFFFFFF'x 
exit_length = d2c(0,4)
exit_data       = '' 
ADDRESS linkpgm "CSNBKGN", 
   'myrc'               'myrs'          , 
   'exit_data_length'   'exit_data'     , 
   'key_form'           'key_length'    , 
   'key_type_1'         'key_type_2'    , 
   'kek_id_1'           'kek_id_2'      , 
   'generated_key_id_1' 'generated_key_id_2' 
 
myrc = c2d(myrc)
myrs = c2d(myrs)                                                                 
IF (myc <> 0 ) THEN 
  DO 
    SAY 'KGN Failed   (rc='myrc' rs='myrs')' 
    Return  myrc myrs 
  END 
                                                                  
Return  myrc myrs c2x(generated_key_id_1)
                                                                         

ADDCKDS

/* -------------------------------------------*/ 
/*  Add CKDS : label and data                 */ 
/* CSNBKRC2 - Key Record Create2              */ 
/* -------------------------------------------*/ 
parse arg label, token 
say "CPBKRC2 " label token 
myrc = 'FFFFFFFF'x 
myrs = 'FFFFFFFF'x 
exit_length =d2c(0,4)
exit_data = '' 
rule_count = d2c(0,4)
rule_array = '' 
token_length = d2c(64,4)
token =x2c(token) 
LEFT(data,64) /* Make sure string length = 64 */ 
ADDRESS LINKPGM "CSNBKRC2", 
   'myrc'          'myrs'            , 
   'exit_length'   'exit_data'       , 
   'rule_count'    'rule_array'      , 
   'label'         'token_length'   , 
   'token'                                                              
myrc = c2d(myrc)
myrs = c2d(myrs)                                                                 
IF (myrc <> 0 ) THEN 
    /* print the return code and description text */
    SAY 'KRC2 Failed   (rc='myrc' rs='myrs')',
             cprs(myrc,myrs)
    RETURN  myrc myrs 
  END 
                                                                 
RETURN   myrc myrs 

and the printable reason code

/* exec to give back reason code string from passed value */ 
parse arg rc,rs 

v.= "Not listed" rs 
v.762="The key values structure for CSNDPKB has a field in error"||, 
            "A length or format is not correct" 
v.2012="The rule_array_count parameter contains a" ||, 
           " number that is not valid." 
v.2016="Rule Array wrong" 
v.2040="Wrong key type.   For example PKI when Importer was expected" 
v.2054="RSA:OAEP optional encoding parameters failed validation" 
v.2089="The algorithm does not match the algorithm"||, 
           " of the key identifier" 
v.10012="Key not found" 
....
return v.rs 

Notes:

I converted from a string to a hex representation of the string when passing data around because the hex data could have a blanks in it. Using the Rexx parse var x a b c parses on blank delimited words, and imbedded blanks could cause a mis-parse.

This is part of the project to set up ICSF so I can create an encrypted dataset on one system, and use it on a different system. This involves setting up keys for encryption, public/private keys and sending stuff between the two systems.

Dataset encryption keys are symmetric and reside in the CKDS.

It took me a while to understand the implications of the fixed and variable format keys, and lots of head scratching when things did not work as expected.

This post is a very simplistic view of the topic – but it should give you enough information to get started with ICSF.

One thing you need to know about (and then quickly forget) is that there are two format of keys.

1. Fixed length – an example of this is a DATA key.
2. Variable length – an example of this is is a CIPHER key.

I just think of there being two versions of APIs – Version 1 for Data and version 2 for Cipher. Any new project should use variable length keys.

You can use either DATA or CIPHER to encrypt a dataset.

Each type of key has its own APIs, so you cannot use a fixed key in an API designed for variable length keys.

Most ICSF APIs have “rules” which are like passing parameters to a command. This is an array of 8 character strings such as “AES “,”PKCS-1.2”,OP “. This string indicates

• AES – encrypt an AES keyType
• PKCS-1.2 using PKCS
• OP “Operational” for use on this system.

When using the APIs’ to export keys, both ends must have matching configuration

For example with a DATA key any one of the following.

1. AES,PKCS-12
2. AES,PKCSOAEP
3. AES,PKCSOAEP,SHA-512

I think the last set of parameters is the strongest.

For CIPHER, this worked

1. AES, PKOAEP2, SHA-256

When programming I found it easier to create some helper routines to reduced the complexity of the APIs. For example I created a ADDKEY routine to specify PKDS|CKDS, the key name, and the buffer contents. As a result I had a high amount of reuse, and my main programs were very compact.

Below I give the API calls for

• Using variable length Cipher keys
  • create the skeleton using CSNBKTB2
  • create the data key using CSNBKGN2
  • export the data key using CSNDSYX
  • import the data key (on another system) using CSNDSYI2
• Using fixed length data keys
  • create the data key using CSNDSYG
  • export the data key using CSNDSYX
  • import the data key (on another system) using CSNDSYI

Using variable length Cipher keys

I see the variable length keys as an evolution in key management from the fixed length keys.

For example you can store the name of the key within the key (though I do not know when or how this is used).

Create the skeleton

I built a skeleton using CSNBKTB2. You can optionally pass in

• a key name
• user data

I did not set these (I set the lengths to zero (&zero)).

I passed in the rule

• char 8 rule[4] = “INTERNAL”,”AES “,”CIPHER “, “ANY-MODE”

The ANY-MODE was required for the encryption to work.

Create the cipher key

I then created the key using CSNBKGN2 and passed in

• char8 rule[2] = {“AES “,”OP “};
• keyLength = 256 ; why use a weaker key?
• char8 keyType1 = {“TOKEN “}; This says use the data passed in from the skeleton token.
• char8 keyType2 = {” “};
• The skeleton data

This returns a block of data (the AES Cipher key encrypted with the local key).

I added it to the local keystore using CSNBKRC2.

Export the cipher key

I exported the key using a public certificate with CSNDSYX. I passed

• the name of the public key.
• char8 rule_array[3] = { “AES “,”PKOAEP2 “,”SHA-256 “}

It returns a block of data containing the AES cipher key encrypted with the public key.

I wrote this data to a file (in binary) and sent it to my remote system.

Import the cipher key at the remote system

I read the file into a buffer, and used CSNDSYI2 to decrypt the contents using the private key, and encrypting it with the local key.

I passed

• char8 rule_array[2] ={“AES “,”PKOAEP2 “}
• the name of the private key
• the buffer

it returned a buffer containing the re-encrypted key

I added it to the keystore on the remote system using CSNBKRC2.

__________________________________________________

If you want to use fixed length keys(why do you?)…

Using fixed length data keys

You can create a data key, and export it at a later date, or you can generate it and export it at the same time.

I feel more comfortable about exporting it when it is needed, in case the “old” copy is out of data.

If you export it from the live system you know it is current.

Create the data key

I used use CSNDSYG

with

• a char 64 key name
• char8 rule[3] = {“AES “, “PKCS-1.2″| PKCSOAEP, “OP “}; If you use PKCSOAEP you can specify SHA-512

This creates a data key in the local repository.

I think PKCSOAEP is better than PKCS-1.2 as is is more recent.

You can also get it to create an RSA enciphered version of the key using a public certificate (as part of key creation) This can be written to a file, and the file sent to the remote system. I tend not to use this, but export the key at the time when wanted. This way you can be sure you have the correct key.

Export the data key

Use CSNDSYX with similar parameters as for the create (CSNDSYG) to create an encrypted version of the Data key.

CSNDSYX returns a block of storage with the encrypted key in it. You can write this to a file in binary or create a base64 encoding of it.

Import the data key

Use CSNDSYI with

• The block of encrypted data (which you can read from a file)
• rule = “AES “, “PKCS-1.2″|| “PKCSOAEP”. If you use PKCSOAEP you can specify SHA-512
• The parameters must match the sending end
• The name of the private key in the PKDS to be used to decrypt the data

This returns a block of data which is the data key, encrypted with the local system’s key.

You can then add it to the CKDS using CSNBKRC2

As part of setting up data set encryption to send data sets between two sites. I wrote some programs to help securely send the symmetric key exchange between two systems using private and public keys.

Basis flow to get a symmetric key on two systems to allow data set encryption and decryption, using private key and public key.

The steps to allow me to send an encrypted dataset to a remote system, using PKI are as follows

1. On the remote system generate a private/public key in the PKDS
2. Extract the public key and send it to the local system
3. Import the public key into the local PKDS
4. On the local system, generate a symmetric AES key for encrypting data sets.
5. Export the key, encrypt it using the public key, into a buffer.
6. Write the buffer to a file
7. Send the file to the remote system.
8. Read the file, decrypt the buffer using the private key, re-encrypt with the local master key, store it in the local CKDS.
9. Displayed the key at each end and compared the
10. Use the symmetric key to decrypt a dataset.

The programs

I wrote some helper programs for example read a key from the CKDS returning the data; create an entry in the PKDS with a specified key and a blob of data containing the token.

Create a private public key

I could not find a batch utility to define a private key, but could use the ISPF panels.

I started writing my own program to do this…

I used API function CSNDPKB. I successfully created a Private/Public key using Elliptic Curve (ECC).

I could display this using the ISPF panels 5 UTILITY->6 PKDS KEYS → 1. This lists all of the keys. Use the line command K to display it. ( D is for delete!). It displays attributes like Algorithm: ECC, size 512, Sections: PRIVATE PUBLIC.

I later found out that ECC cannot be used to encrypt a symmetric AESkey. “Use the Symmetric Key Export callable service to transfer an application-supplied AES, DES or variable length symmetric key token key from encryption under a master key to encryption under an application supplied RSA public key or AES EXPORTER key. I could not find how to generate an EXPORTER key with public certificate.

I tried using CSNDPKB to create an RSA private key. You have to complete a “Key Value Structure”. I struggled to complete this for RSA because I needed to specify “prime number p”,and “prime number q”. Ive since found how to do this. I tried an alternate approach of using the ISPF panels.

On the remote system, I used the ISPF panels to create a PKI key. 5 UTILITY → 6 PKDS KEYS → 6 Generate PKA keys. I created a new RSA key with bit length 4096, as bit length 512 was too weak.

Having created my private/public key, I used the ISPF panels to export the public key to a data set, sent it to my local system and import it using the ISPF panels. This public key does not need to be sent securely.

• You can extract the contents of this file using RACDCERT ADD(‘COLIN.EXPORT.ECC1’) ID(COLIN). This gave me a key with

Certificate ID: 2QXD1tPJ1dPBwsXT8PDw8PDw8PFA
Status: TRUST
Start Date: 2021/08/29 09:42:44
End Date: 2041/08/29 09:42:44
Serial Number:
>00< 
Issuer's Name: >CN=ECCB512Z< 
Subject's Name: >CN=ECCB512Z<
Signing Algorithm: sha256ECDSA
Key Type: Brainpool ECC
Key Size: 512
Private Key: NO
Ring Associations:

I had now had a private key at the remote end, and the public certificate at the local end.

I can encrypt at the local end using the public key, and decrypt it at the remote end using the private key.

Create the AES symmetric key on the local end.

I found I could not use AES type DATA, and so had to use AES type CIPHER.

If I used KGUP utility with

ADD TYPE(CIPHER ) ALGORITHM(AES) LENGTH(32) LAB(AESCIPHER)

This could not be used to encrypt because it gave IEC143I 213-85 RC=X’00000008′, RSN=X’0000085E’

85E (2142) The key usage attributes of the variable-length key token does not allow the requested operation. For example, the request might have been to encrypt data, but encryption is not allowed, or the request might have been to use the ECB cipher mode, but that mode is not allowed.

When I displayed through the ISPF panels (5.5.1) it it showed

Key Usage: ENCRYPT DECRYPT CBC

If I generated an AES key using the API, I found that ENCRYPT DECRYPT ANY-MODE worked, but I could not see how to set ANY-MODE using KGUP.

Program to generate an AES key

 // build the skeleton.   It is returned in pToken
 rc = skeletonAES(&pToken,& lToken); 
 if ( rc != 0 ) return rc; 
 
 // input: the skeleton 
 // output: the token 
 rc = GENAES2(pToken,&lToken); 
 if ( rc != 0 ) return rc; 

 // add it to the CKDS                                                           
 rc = doAdd2("C",pKey,pToken,lToken,pDelete); 
 if ( rc != 0 ) return rc; 
 return rc; 

skeletonAES program

// this program allocates storage, uses it, and passes it back
// to the caller. 
int skeletonAES(char ** pData, int * lData) 
 { 
  int rc; 
  int rs; 
  int zero = 0; 
  int rule_count                 =  4 ; 
  char8 rule[ 4] ={ 
   "INTERNAL","AES     ","CIPHER  ",    "ANY-MODE" 
   }; 
  char * pRule = & rule[0][0];
  int lKeyToken=725; 
  char * pKeyToken; 
  pKeyToken = (char *) malloc(lKeyToken); 
  CSNBKTB2(   
           &rc,         /* return code             */ 
           &rs,         /* reason code             */ 
           &zero,       /* exit data length        */ 
           0,           /* exit data[]             */ 
           &rule_count, /* rule array count        */ 
           pRule,       /* rule array[]            */ 
           &zero,       /* clear key bit length    */ 
           0,           /* key value[]             */ 
           &zero,       /* key name length         */ 
           0,           /* key name[64]            */ 
           &zero,       /* user assoc data length  */ 
           0,           /* user associated data[]  */ 
           &zero,       /* token data length       */ 
           0,           /* token data[]            */ 
           &zero,       /* service data length     */ 
           0,           /* service data[]          */ 
           &lKeyToken,  /* target key token length */ 
           pKeyToken ); /* target key token[]      */ 
 if ( rc > 0) 
 { 
    printf("CSNBKTB2 rc %i rs %i %s\n",rc,rs,csfgetrc(rs)); 
    return rc; 
 } 
 
   free (pData); // get rid of the passed in block 
// return the length
 *lData = lKeyToken;
//pass back the address of the token
 *pData = pKeyToken; 
 printf("skeletonAES key length %i\n",lKeyToken); 
// printHex(stdout,&keyToken,lKeyToken); 
   printAES((char *) pKeyToken,lKeyToken); 
   return 0; 
} 

Create program keygenerate

// this takes the data passed in, and uses it
// The length is updated.
int keyGenerate2( char * pData, int *  lData) 
{ 
  int rc; 
  int rs; 
  int zero = 0; 
  int rule_count                 =  2; 
  // key type AES and used for OP (on this system 
  char8 rule[2]  = {"AES     ","OP      "}; 
  char * pRule = &rule[0][0];
  int keyLength = 256 ;//  AES 256  - why use any other? 
                                                                            
  char8  keyType1 = {"TOKEN   "}; 
  char8  keyType2 = {"        "}; 
  int i64 = 64; 
  int l725 = 725; 

 CSNBKGN2( 
         &rc  ,        /* return code             */ 
         &rs  ,        /* reason code             */ 
         &zero,        /* exit data length        */ 
         0,            /* exit data[]             */ 
         &rule_count,  /* rule array count        */ 
         pRule,        /* rule array[]            */ 
         &keyLength,   /* clear key bit length    */ 
(char *) &keyType1   , /* key type1[8]            */ 
(char *) &keyType2   , /* key type2[8]            */ 
         &zero,        /* key name1 length        */ 
         0,            /* key name1[64]           */ 
         &zero,        /* key name2 length        */ 
         0,            /* key name2[64]           */ 
         &zero,        /* user assoc data1 length */ 
         0,            /* user associated data1[] */ 
         &zero,        /* user assoc data2 length */ 
         0,            /* user associated data2[] */ 
         &zero,        /* KEK id1 length          */ 
         0,            /* KEK id1[]               */ 
         &zero,        /* KEK id2 length          */ 
         0,            /* KEK id2[]               */ 
         &l725,        /* output key id1 length   */ 
 (char *)pData,        /* output key id1[]        */ 
         &zero    ,    /* output key id2 length   */ 
         0          ); /* output key id2[]        */ 
  if ( rc > 0) 
  { 
    printf("CSNBKGN2 rc %i rs %i %s\n",rc,rs,csfgetrc(rs)); 
    return rc; 
  } 
  *lData = l725; 
  // the same buffer is used,so no need to set pData
  return rc; 
} 

Using these and my add2(…) functions I could create my AES for CIPHER with ANY-MODE. (See ANY-MODE above).

Export the AES key

To export the AES key, you need the name of the public key.

You need a different set of rules for a DATA key and a CIPHER key.

 int   lData; 
 char * pData; 
 rc =doExportAES (pKey,pPublic,pType,&pData, &lData); 
 if (rc > 0 ) return rc; 
 rc = writeKey(dd,pData,lData); 
 if (rc > 0 ) return rc; 

I created a routine which read the key, and one to write it to a file.

The parameters to doExportAES are

• dd name “dd:CERT would use //CERT .. in the JCL
• key is a char64 left justified key name in the CKDS
• pPublic a char 64 left justified name of the public key to use. It must exit in the PKDS.
• A pointer to the string to containing the data
• The length of the returned data.

int doExportAES (char * pKey, char * pPublic, char * pType, 
                 char ** pData, int * lData)  
{ 
  int rc; 
  int rs; 
  int i64 = 64; 
  int zero = 0; 
  int rule_count                 =  3; 
  char8 rule_Cipher[3] = 
                     {"AES     ", 
                      "PKOAEP2 ", 
                      "SHA-256 "}; 
  char * pRule =   rule_Cipher[0][0];
  int lOut = 900; 
  char * pOut; 
  pOut = (char * ) malloc(lOut); 
  printf("Source Key user   %64.64s.\n",key  ); 
  printf("Transport key     %64.64s.\n",encrypt); 

   CSNDSYX ( 
            &rc,                /* return code            */ 
            &rs ,               /* reason code            */ 
            &zero,              /* exit data length       */ 
            0    ,              /* exit data[]            */ 
            &rule_count,        /* rule array count       */ 
            pRule,              /* rule array[]           */ 
            &i64   ,            /* source key    length,  */ 
            pKey  ,             /* source key             */ 
            &i64,               /* RSA public key length  */ 
            pPublic,            /* RSA public key token   */ 
            &lOut,              /* exported key length    */ 
            pOut           );   /* exported key           */ 

if( rc > 0) 
  printf("CSNDSYX  rc %i rs %i %s\n",rc,rs,csfgetrc(rs)); 
if (rc != 0) return rc; 

// return the exported data

 *pData = pOut; 
* lData = lOut; 
   return 0; 
} 

Import the certificate at the remote end

I created IMPAES

  rc=  read(dd,&pData,&lData);         // returns a buffer  from the file
  printf("readCert rc %i data length %i\n",rc,lData ); 
  if ( rc != 0) return 8; 

  rc = doImportAES(pKey,pPrivateKey,&pData,&lData); 
  if ( rc != 0) return 8; 
  printf("Returned buffer size %i\n",lData); 
  rc = doAdd2("C",  pKey,pData,lData); 
  if ( rc != 0 ) return rc; 
  return 0; 

read opens the ddname , and gets back the (binary) data in pData of length lData.

This get passed to doImportAES which uses the private key pointed to by pPrivateKey (a 64 char left justified string). This then returns the AES key (encrypted with the local key) which is then added using do ADD2.

DoImportAES.

/* --------------------------------------------------------------- *
/* Import public key                                               *
/* --------------------------------------------------------------- *
int doImportAES (char * pKey, char * pDecryptKey, 
    char ** pData, int * lData) 
{ 
  int rc; 
  int rs; 
  int zero = 0; 
  int i64 = 64; 
  int rule_count                 =  2; 
  char8 rule_array[2]            ; 
  memcpy(&rule_array[0],"AES     ",8); 
  memcpy(&rule_array[1],"PKOAEP2 ",8); 
  int lOutput = 725 ; 
  char * pOutput = (char * ) malloc(lOutput); 
  if ( pOutput == 0) 
  { 
    printf("malloc for %i failed in IMPAES\n",lOutput); 
  } 
  printf("Key %64.64s.\n",pKey); 
  printf("Decrypt Key %64.64s.\n",pDecryptKey); 
  printf("lInput  %i\n",*lData     ); 
//printHex(stdout,* pData,32); 
  CSNDSYI2 ( 
              &rc,           /* return code            */ 
              &rs ,          /* reason code            */ 
              &zer           /* exit data length       */ 
              0    ,         /* exit data[]            */ 
              &rule_count,   /* rule array count       */ 
   (char *)   &rule_array[0],/* rule array[]           */ 
              lData     ,    /* length of input data   */ 
            * pData,         /* input data             */ 
              &i64,          /* cca DES token length,  */ 
   (char *)   pDecryptKey ,  /* cca DES token[64]      */ 
              &i64,          /* key name length        */ 
   (char *)   pKey,          /* key name[]             */ 
              &lOutput    ,  /* Imported key length    */ 
   (char *)   pOutput   );   /* Imported key           */ 
// if( rc > 0) 
   printf("CSNDSYI2 rc %i rs %i %s\n",rc,rs,csfgetrc(rs)); 
 if (rc != 0) return rc; 

 // get rid of input buffer 
   printf("CSNDSYI2 data lengt %i\n",lOutput); 
   free (*pData); 
// and update with the new data
   *pData =  pOutput; 
   *lData = lOutput; 
 return 0; 
 } 

All this creates a key in the CKDS on the remote system which I could use to decrypt a data set.

Summary

It took a long time to write these programs, because I did not know the path to take, and went down many dead ends. Once you know the concepts and know which ICSF functions and options you need, it is not too difficult.

Having these helper routines, I was able to create a program to generate a symmetric key using Diffi-Hellman in about 2 hours! (Most of this time was reading the documentation).

I was exploring data set encryption, and wanted to copy some data to an encrypted data set, and move to a new z/OS system (on a different USB). I used this as an exercise to learn about ICSF.

Overview

ICSF has lots of APIs to do wonderful things with encryption such as checking PIN numbers and encrypting packets of data. It also has some commands to define keys etc.

It was easy to set up data set encryption on one system. It was hard to set it up as a typical customer, where you had to set up two independent systems and send files between them.

The administration guide describes a scenario of two ICSF systems establishing initial transport keys. This was a bit clumsy. You have to edit a file, extract a string of hex digits and use a courier to send them to the remote system.

I set myself the challenge to use private and public keys to securely transfer the keys from one system to another. I could not find any commands to help me do this – so I had to write my own.

It took me much longer than expected, partly because I am not a good C programmer, but also because the path was not clear, and it took a while to understand what I needed to do. For example some APIs work with a key with type of DATA, and some do not. I ended up using a key type of CIPHER because that was the only one I could get to work. I’ve since got DATA to work.

Background ICSF information.

It took me a few days to understand the ICSF environments.

• You have Symmetric keys – where a key is used for encryption, and the same key is used for decryption. These keys are stored in the Cryptographic Key Data Set (CKDS). These have two formats (and use different APIs) –
  • fixed length
  • variable length – this is a follow-on from fixed lengths and should be used instead of fixed lengths.
• You have Asymmetric keys – for example private and public PKI keys. Everyone can have access to the public key. Only you have access to your private key. These are stored in the PKDS (Public Key Data Set). There are different flavours of PKI keys using different algorithm, and key sizes.
• The ICSF API documentation refers to labels and tokens
  • Labels are a 64 character string used to identify the record in the +KDS.
  • Tokens represent the actual key, and is a structure (or blob of data). For example an AES token has information on the hash algorithm used, the encryption algorithm used, what sort of key it is (data, cipher, exporter). You can generate a token, use it, and not write it to the +KDS.
  • Sometimes a field in the API can be the label, or the token. If the length is 64 it is a label, otherwise it is a token.
• Keys
  • Internal Keys in the +KDS are encrypted by a master level of encryption. If you you want to decrypt using a particular key. The (encrypted) key is extracted from the key store, and passed to the hardware encryption. The hardware decrypts the key, then uses it to decrypt the data. The unencrypted key does not leave the hardware.
  • External keys are keys that have not been encrypted, or are encrypted with a encrypted under a key-encrypting key (KEK) in the +KDS other than the master key. To use it you have to give the name/token of the KEK along with the name/token of external key.
• You can say “extract the key, and encrypt it using another key before giving it to me”. You can then send the encrypted key to another system, which can decrypt the key and use it. The plain text of the key is never seen.
• You can do things in the API which you are not authorised to do in the ISPF panels.
• I was able to extract AES keys, encrypt them with Public/Private keys for transportation, and import them at the remote system. This is not considered good practice because the IBM cryptographic standards say you should keep keys used for encrypting data separate from those used to transmit keys. These are known as Key Transport Keys, and you have Exported and Importer keys. The documentation talks about Key Encryption Keys (KEKs) which is another name for the Key Transport Keys. You should have these for production, but I managed without them for my investigations. All these “keys” in a sentence made my head ache!

The hardest part

I found the hardest part about using ICSF was knowing which options to specify. For example you can use a public/private key to extract a key used for data set encryption, send it to the remote site, and decrypt it and add it to the system. How should you set it up? The answers are all in the documentation – somewhere, there is no getting started guide. The questions I had included:

What encryption technique and key strength should I use for data set encryption?

ICSF supports two techniques for symmetric encryption

1. DES – Data Encryption Standard
2. AES – Advanced Encryption Standard. This is often considered to be better than DES.

With each of these you can have different strength keys.

To encrypt data sets you need to use AES 256.

What sort of private/public key do I need

You can create a private/public pair of keys using

1. RSA
   1. Modulus-exponent form (with a variety of different length modulus)
   2. Chinese Remainder Theorem(RCT) (with a variety of different length modulus)
2. ECC (Elliptical curves)
   1. With a variety of curves: NIST, Prime, Brainpool
   2. And a variety of sizes
3. CRYSTALS-Dilithium. Not having heard of this, I looked it up. It serves as a controlling agent in the faster than light warp drive in Star Trek, as well as being a technique for encryption.

Only RSA is supported to encrypt an AES key to send to a remote system using PKI.

What encryption technique should I use?

There are different ways of encrypting using an RSA key.

1. PKCS–1.2 – RSA DSI PKCS #1 block type 02
2. PKCSOAEP – RSA DSI PKCS #1V2 OAEP
3. PKOAEP2 – RSA DSI PKCS #1 v2.1 RSAES-OAEP documentation (Not valid with DATA keys)

3. is better than 2. which is better than 1.

I use PKOAEP2 for CIPHER keys, and PKCSOAEP for DATA keys.

It would be very good if there was a documented decision tree giving the best advice on the options to use, along the lines of

1. If you want to do data set encryption use AES256 and use CIPHER rather than DATA.
2. If you want to encrypt a key to send to a remote system use RSA, with key size > … (eg 4096)
3. …..

ICSF programming model

I had used the RACF callable services R_datalib (Certificate Data Library) to manage digital certificates. There is one module, and you pass parameters to define what to do, function_code = 0x01: get first, function code 0x0a: delete keyring. The parameters are similar.

With ICSF there are many functions, and the parameters are different. Although I was expecting a function “create public key and store it in the database with this name”, there may be times when you want to create a public key, use it and not store it in the database.

When you consider the options, using just one API does not work.

Low level functions

ICSF provides functions for each logical function. for example:

1. create key (several flavours)
2. store key in *KDS (several flavours)
3. extract key (several flavours)
4. encrypt data using this public key token (big blob of data), or use this label of a public key in the PKDS.

Rules

You pass configuration through to routines using “rules”. For example

typedef char char8[8];

int rule_count = 4 ;

char8 rule[ 4] ={ “AES “, “INTERNAL”, “CIPHER “, “ANY-MODE” };

These are like passing parameters through a command interface. It was easy to do – and worked well.

These parameters mean

1. Create an AES key (the choice is AES or HMAC)
2. Create an INTERNAL format token which will be used on this machine.
3. Create a key with type of CIPHER. There is a choice of 8 options.
4. ANY-MODE: Specifies that this key can be used for any encryption mode. The default is CBC:Specifies that this key can be used for cipher block chaining.

Using the rules was easy – finding which rules to use was hard (as I mentioned above).

Return and reason codes

Each function provides a return code, and a reason code. There is no service to call which returns a short string describing the error from the reason code. I wrote my own.

Exit programs

You can pass information through to an exit program – this feels like a very advanced topic. I haven’t used it.

Using the functions

The ICSF functions call stub services (which jump into the ICSF address space). These services do not have much function in them. You should not have to recompile your programs, or rebind them if you use a different level of ICSF.

C coding

With C routines you might code

printf(“the number is %\n”,i);

and pass “i” in.

With the stub interface you have to pass in the address of the variables for example

int zero = 0;

rc= CSNDPKB (&rc, &rs, &zero…)…

I found it easiest to put each ICSF function into its own function and call that, so hiding a lot of the ICSF API, and using common C techniques.

Rexx coding

It is pretty easy to write in Rexx. The hardest part is knowing which options to use.

The disadvantage of using Rexx, is that people could turn trace on, and display sensitive information.

Writing my own helper interface

I created routines like rc= skeletonAES(char ** pData, int * lData) {} to do the work, and return storage with the data in it.

Memory management: Within this routine I did a malloc() request for the storage. It passed the storage to ICSF, and returned the address back to the caller. I could have passed in a block of storage, but this means the higher level function needs to know length of the storage required. I think having the lower level function allocate the storage is better, because the routine knows the length it needs and makes it self contained.

int skeletonAES(char ** pData, int * lData) {

int lStorage = 725;
char *pStorage = malloc(lStorage);
CSNBKTB2(&rc, &rs,
…
     &zero,         /* service data length     */ 
     0,             /* service data[] ignored  */ 
     &lKeyToken,    /* target key token length */ 
     pKeyToken   ); /* target key token[]      */ 

*pData = pStorage;
* lData = lStorage;  // return the  true length 
                     //  of data returned.
return rc 
}

Once I had finished with the storage I could use free(…) to release the block.

What helper routines did I create?

I found it useful to create some helper routines.

Read the *KDS

rc=read(“C”,pKey, pData, lData );

rc= read(“P”,pKey, pData, lData );

to read the record and return a pointer to the data.
Internally

• If “C” then use CSNBKRR2.
• If “P” then use CSNDKRR.

I wrote some Rexx helper functions: readCKDS(label) and readPKDS(label), returning the return code, reason code, and the data.

doExists

rc=doExists(“C”,pKey );

rc= doExists(“P”,pKey );

to read the record and return if the record was not found.
If “C” then use CSNBKRR2.

If “P” then use CSNDKRR.

This is actually a wrapper around read, passing back the return code.

Add

rc = doAdd2(“C”,pKey,pReplace,Token ,lToken );

If “C” then use CSNBKRC2.

If “P” then use CSNDKRC.

If the add got the return code “already exists”, and pReplace = “yes” , then delete the record and retry the add.

In rexx I wrote addCKDS(label,data) and addPKDS(label,data).

PrintHex(stdout,pData,lData)

To print a dump like format of a block of storage.

PrintAES(pData,lData))

to print a summary of the AES token.

WriteKey

rc = writekey(dd,pData,lData)

This writes the data to a file specified by dd. Where dd is a string used in fopen, such as “dd:cert”.

The dataset was a variable length, with just one on record in it.

ReadKey

rc = readkey(dd,&pData,&lData)

This reads one record from the file specified by dd. Where dd is a string used in fopen, such as “dd:cert”. It allocates storage, and passes it back to the caller.

Other helpers

• Export PKI public certificate
• Import PKI public certificate
• Create AES Skeleton for CIPHER (Variable format key)
• Create AES Skeleton for DATA(Fixed format key)
• Generate symmetric key using Diffi-Hellman
• Export AES CIPHER key (Variable format key)
• Export AES DATA key(Fixed format key)
• Import AES CIPHER key (Variable format key)
• Import AES DATA key(Fixed format key)

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