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 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 #ifdef FREEBL_NO_DEPEND

 #include "stubs.h"

 #endif

 #include "blapit.h"

 #include "blapii.h"

 #include "cts.h"

 #include "secerr.h"

 struct CTSContextStr {

     freeblCipherFunc cipher;

     void *context;

     /* iv stores the last ciphertext block of the previous message.

      * Only used by decrypt. */

     unsigned char iv[MAX_BLOCK_SIZE];

 };

 CTSContext *

 CTS_CreateContext(void *context, freeblCipherFunc cipher,

 		  const unsigned char *iv, unsigned int blocksize)

 {

     CTSContext  *cts;

     if (blocksize > MAX_BLOCK_SIZE) {

 	PORT_SetError(SEC_ERROR_LIBRARY_FAILURE);

 	return NULL;

     }

     cts = PORT_ZNew(CTSContext);

     if (cts == NULL) {

 	return NULL;

     }

     PORT_Memcpy(cts->iv, iv, blocksize);

     cts->cipher = cipher;

     cts->context = context;

     return cts;

 }

 void

 CTS_DestroyContext(CTSContext *cts, PRBool freeit)

 {

     if (freeit) {

 	PORT_Free(cts);

     }

 }

 /*

  * See addemdum to NIST SP 800-38A

  * Generically handle cipher text stealing. Basically this is doing CBC

  * operations except someone can pass us a partial block.

  *

  *  Output Order:

  *  CS-1:  C1||C2||C3..Cn-1(could be partial)||Cn   (NIST)

  *  CS-2: pad == 0 C1||C2||C3...Cn-1(is full)||Cn   (Schneier)

  *  CS-2: pad != 0 C1||C2||C3...Cn||Cn-1(is partial)(Schneier)

  *  CS-3: C1||C2||C3...Cn||Cn-1(could be partial)   (Kerberos)

  *

  * The characteristics of these three options:

  *  - NIST & Schneier (CS-1 & CS-2) are identical to CBC if there are no

  * partial blocks on input.

  *  - Scheier and Kerberos (CS-2 and CS-3) have no embedded partial blocks,

  * which make decoding easier.

  *  - NIST & Kerberos (CS-1 and CS-3) have consistent block order independent

  * of padding.

  *

  * PKCS #11 did not specify which version to implement, but points to the NIST

  * spec, so this code implements CTS-CS-1 from NIST.

  *

  * To convert the returned buffer to:

  *   CS-2 (Schneier): do

  *       unsigned char tmp[MAX_BLOCK_SIZE];

  *       pad = *outlen % blocksize;

  *       if (pad) {

  *          memcpy(tmp, outbuf+*outlen-blocksize, blocksize);

  *          memcpy(outbuf+*outlen-pad,outbuf+*outlen-blocksize-pad, pad);

  *	    memcpy(outbuf+*outlen-blocksize-pad, tmp, blocksize);

  *       }

  *   CS-3 (Kerberos): do

  *       unsigned char tmp[MAX_BLOCK_SIZE];

  *       pad = *outlen % blocksize;

  *       if (pad == 0) {

  *           pad = blocksize;

  *       }

  *       memcpy(tmp, outbuf+*outlen-blocksize, blocksize);

  *       memcpy(outbuf+*outlen-pad,outbuf+*outlen-blocksize-pad, pad);

  *	 memcpy(outbuf+*outlen-blocksize-pad, tmp, blocksize);

  */

 SECStatus

 CTS_EncryptUpdate(CTSContext *cts, unsigned char *outbuf,

 		unsigned int *outlen, unsigned int maxout,

 		const unsigned char *inbuf, unsigned int inlen,

 		unsigned int blocksize)

 {

     unsigned char lastBlock[MAX_BLOCK_SIZE];

     unsigned int tmp;

     int fullblocks;

     int written;

     SECStatus rv;

     if (inlen < blocksize) {

 	PORT_SetError(SEC_ERROR_INPUT_LEN);

 	return SECFailure;

     }

     if (maxout < inlen) {

 	*outlen = inlen;

 	PORT_SetError(SEC_ERROR_OUTPUT_LEN);

 	return SECFailure;

     }

     fullblocks = (inlen/blocksize)*blocksize;

     rv = (*cts->cipher)(cts->context, outbuf, outlen, maxout, inbuf,

 	 fullblocks, blocksize);

     if (rv != SECSuccess) {

 	return SECFailure;

     }

     *outlen = fullblocks; /* AES low level doesn't set outlen */

     inbuf += fullblocks;

     inlen -= fullblocks;

     if (inlen == 0) {

 	return SECSuccess;

     }

     written = *outlen - (blocksize - inlen);

     outbuf += written;

     maxout -= written;

     /*

      * here's the CTS magic, we pad our final block with zeros,

      * then do a CBC encrypt. CBC will xor our plain text with

      * the previous block (Cn-1), capturing part of that block (Cn-1**) as it

      * xors with the zero pad. We then write this full block, overwritting

      * (Cn-1**) in our buffer. This allows us to have input data == output

      * data since Cn contains enough information to reconver Cn-1** when

      * we decrypt (at the cost of some complexity as you can see in decrypt

      * below */

     PORT_Memcpy(lastBlock, inbuf, inlen);

     PORT_Memset(lastBlock + inlen, 0, blocksize - inlen);

     rv = (*cts->cipher)(cts->context, outbuf, &tmp, maxout, lastBlock,

 			blocksize, blocksize);

     PORT_Memset(lastBlock, 0, blocksize);

     if (rv == SECSuccess) {

 	*outlen = written + blocksize;

     }

     return rv;

 }

 #define XOR_BLOCK(x,y,count) for(i=0; i < count; i++) x[i] = x[i] ^ y[i]

 /*

  * See addemdum to NIST SP 800-38A

  * Decrypt, Expect CS-1: input. See the comment on the encrypt side

  * to understand what CS-2 and CS-3 mean.

  *

  * To convert the input buffer to CS-1 from ...

  *   CS-2 (Schneier): do

  *       unsigned char tmp[MAX_BLOCK_SIZE];

  *       pad = inlen % blocksize;

  *       if (pad) {

  *          memcpy(tmp, inbuf+inlen-blocksize-pad, blocksize);

  *          memcpy(inbuf+inlen-blocksize-pad,inbuf+inlen-pad, pad);

  *	    memcpy(inbuf+inlen-blocksize, tmp, blocksize);

  *       }

  *   CS-3 (Kerberos): do

  *       unsigned char tmp[MAX_BLOCK_SIZE];

  *       pad = inlen % blocksize;

  *       if (pad == 0) {

  *           pad = blocksize;

  *       }

  *       memcpy(tmp, inbuf+inlen-blocksize-pad, blocksize);

  *       memcpy(inbuf+inlen-blocksize-pad,inbuf+inlen-pad, pad);

  *	 memcpy(inbuf+inlen-blocksize, tmp, blocksize);

  */

 SECStatus

 CTS_DecryptUpdate(CTSContext *cts, unsigned char *outbuf,

 		unsigned int *outlen, unsigned int maxout,

 		const unsigned char *inbuf, unsigned int inlen,

 		unsigned int blocksize)

 {

     unsigned char *Pn;

     unsigned char Cn_2[MAX_BLOCK_SIZE]; /* block Cn-2 */

     unsigned char Cn_1[MAX_BLOCK_SIZE]; /* block Cn-1 */

     unsigned char Cn[MAX_BLOCK_SIZE];   /* block Cn   */

     unsigned char lastBlock[MAX_BLOCK_SIZE];

     const unsigned char *tmp;

     unsigned int tmpLen;

     int fullblocks, pad;

     unsigned int i;

     SECStatus rv;

     if (inlen < blocksize) {

 	PORT_SetError(SEC_ERROR_INPUT_LEN);

 	return SECFailure;

     }

     if (maxout < inlen) {

 	*outlen = inlen;

 	PORT_SetError(SEC_ERROR_OUTPUT_LEN);

 	return SECFailure;

     }

     fullblocks = (inlen/blocksize)*blocksize;

     /* even though we expect the input to be CS-1, CS-2 is easier to parse,

      * so convert to CS-2 immediately. NOTE: this is the same code as in

      * the comment for encrypt. NOTE2: since we can't modify inbuf unless

      * inbuf and outbuf overlap, just copy inbuf to outbuf and modify it there

      */

     pad = inlen - fullblocks;

     if (pad != 0) {

 	if (inbuf != outbuf) {

 	    memcpy(outbuf, inbuf, inlen);

 	    /* keep the names so we logically know how we are using the

 	     * buffers */

 	    inbuf = outbuf;

 	}

 	memcpy(lastBlock, inbuf+inlen-blocksize, blocksize);

 	/* we know inbuf == outbuf now, inbuf is declared const and can't

 	 * be the target, so use outbuf for the target here */

 	memcpy(outbuf+inlen-pad, inbuf+inlen-blocksize-pad, pad);

 	memcpy(outbuf+inlen-blocksize-pad, lastBlock, blocksize);

     }

     /* save the previous to last block so we can undo the misordered

      * chaining */

     tmp =  (fullblocks < blocksize*2) ? cts->iv :

 			inbuf+fullblocks-blocksize*2;

     PORT_Memcpy(Cn_2, tmp, blocksize);

     PORT_Memcpy(Cn, inbuf+fullblocks-blocksize, blocksize);

     rv = (*cts->cipher)(cts->context, outbuf, outlen, maxout, inbuf,

 	 fullblocks, blocksize);

     if (rv != SECSuccess) {

 	return SECFailure;

     }

     *outlen = fullblocks; /* AES low level doesn't set outlen */

     inbuf += fullblocks;

     inlen -= fullblocks;

     if (inlen == 0) {

 	return SECSuccess;

     }

     outbuf += fullblocks;

     maxout -= fullblocks;

     /* recover the stolen text */

     PORT_Memset(lastBlock, 0, blocksize);

     PORT_Memcpy(lastBlock, inbuf, inlen);

     PORT_Memcpy(Cn_1, inbuf, inlen);

     Pn = outbuf-blocksize;

     /* inbuf points to Cn-1* in the input buffer */

     /* NOTE: below there are 2 sections marked "make up for the out of order

      * cbc decryption". You may ask, what is going on here.

      *   Short answer: CBC automatically xors the plain text with the previous

      * encrypted block. We are decrypting the last 2 blocks out of order, so

      * we have to 'back out' the decrypt xor and 'add back' the encrypt xor.

      *   Long answer: When we encrypted, we encrypted as follows:

      *       Pn-2, Pn-1, (Pn || 0), but on decryption we can't

      *  decrypt Cn-1 until we decrypt Cn because part of Cn-1 is stored in

      *  Cn (see below).  So above we decrypted all the full blocks:

      *       Cn-2, Cn,

      *  to get:

      *       Pn-2, Pn, Except that Pn is not yet corect. On encrypt, we

      *  xor'd Pn || 0  with Cn-1, but on decrypt we xor'd it with Cn-2

      *  To recover Pn, we xor the block with Cn-1* || 0 (in last block) and

      *  Cn-2 to get Pn || Cn-1**. Pn can then be written to the output buffer

      *  and we can now reunite Cn-1. With the full Cn-1 we can decrypt it,

      *  but now decrypt is going to xor the decrypted data with Cn instead of

      *  Cn-2. xoring Cn and Cn-2 restores the original Pn-1 and we can now

      *  write that oout to the buffer */

     /* make up for the out of order CBC decryption */

     XOR_BLOCK(lastBlock, Cn_2, blocksize);

     XOR_BLOCK(lastBlock, Pn, blocksize);

     /* last buf now has Pn || Cn-1**, copy out Pn */

     PORT_Memcpy(outbuf, lastBlock, inlen);

     *outlen += inlen;

     /* copy Cn-1* into last buf to recover Cn-1 */

     PORT_Memcpy(lastBlock, Cn_1, inlen);

     /* note: because Cn and Cn-1 were out of order, our pointer to Pn also

      * points to where Pn-1 needs to reside. From here on out read Pn in

      * the code as really Pn-1. */

     rv = (*cts->cipher)(cts->context, Pn, &tmpLen, blocksize, lastBlock,

 	 blocksize, blocksize);

     if (rv != SECSuccess) {

 	return SECFailure;

     }

     /* make up for the out of order CBC decryption */

     XOR_BLOCK(Pn, Cn_2, blocksize);

     XOR_BLOCK(Pn, Cn, blocksize);

     /* reset iv to Cn  */

     PORT_Memcpy(cts->iv, Cn, blocksize);

     /* This makes Cn the last block for the next decrypt operation, which

      * matches the encrypt. We don't care about the contexts of last block,

      * only the side effect of setting the internal IV */

     (void) (*cts->cipher)(cts->context, lastBlock, &tmpLen, blocksize, Cn,

 		blocksize, blocksize);

     /* clear last block. At this point last block contains Pn xor Cn_1 xor

      * Cn_2, both of with an attacker would know, so we need to clear this

      * buffer out */

     PORT_Memset(lastBlock, 0, blocksize);

     /* Cn, Cn_1, and Cn_2 have encrypted data, so no need to clear them */

     return SECSuccess;

 }