/********************************************************************************/ /* */ /* Message Authentication Codes Based on a Symmetric Block Cipher */ /* Written by Ken Goldman */ /* IBM Thomas J. Watson Research Center */ /* $Id: CryptCmac.c 1658 2021-01-22 23:14:01Z kgoldman $ */ /* */ /* Licenses and Notices */ /* */ /* 1. 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These functions only use the single block encryption functions of the selected symmetric cryptographic library. */ /* 10.2.6.2 Includes, Defines, and Typedefs */ #define _CRYPT_HASH_C_ #include "Tpm.h" #include "CryptSym.h" #if ALG_CMAC /* 10.2.6.3 Functions */ /* 10.2.6.3.1 CryptCmacStart() */ /* This is the function to start the CMAC sequence operation. It initializes the dispatch functions for the data and end operations for CMAC and initializes the parameters that are used for the processing of data, including the key, key size and block cipher algorithm. */ UINT16 CryptCmacStart( SMAC_STATE *state, TPMU_PUBLIC_PARMS *keyParms, TPM_ALG_ID macAlg, TPM2B *key ) { tpmCmacState_t *cState = &state->state.cmac; TPMT_SYM_DEF_OBJECT *def = &keyParms->symDetail.sym; // if(macAlg != TPM_ALG_CMAC) return 0; // set up the encryption algorithm and parameters cState->symAlg = def->algorithm; cState->keySizeBits = def->keyBits.sym; cState->iv.t.size = CryptGetSymmetricBlockSize(def->algorithm, def->keyBits.sym); MemoryCopy2B(&cState->symKey.b, key, sizeof(cState->symKey.t.buffer)); // Set up the dispatch methods for the CMAC state->smacMethods.data = CryptCmacData; state->smacMethods.end = CryptCmacEnd; return cState->iv.t.size; } /* 10.2.5.3.2 CryptCmacData() */ /* This function is used to add data to the CMAC sequence computation. The function will XOR new data into the IV. If the buffer is full, and there is additional input data, the data is encrypted into the IV buffer, the new data is then XOR into the IV. When the data runs out, the function returns without encrypting even if the buffer is full. The last data block of a sequence will not be encrypted until the call to CryptCmacEnd(). This is to allow the proper subkey to be computed and applied before the last block is encrypted. */ void CryptCmacData( SMAC_STATES *state, UINT32 size, const BYTE *buffer ) { tpmCmacState_t *cmacState = &state->cmac; TPM_ALG_ID algorithm = cmacState->symAlg; BYTE *key = cmacState->symKey.t.buffer; UINT16 keySizeInBits = cmacState->keySizeBits; tpmCryptKeySchedule_t keySchedule; TpmCryptSetSymKeyCall_t encrypt; // // Set up the encryption values based on the algorithm switch (algorithm) { FOR_EACH_SYM(ENCRYPT_CASE) default: FAIL(FATAL_ERROR_INTERNAL); } while(size > 0) { if(cmacState->bcount == cmacState->iv.t.size) { ENCRYPT(&keySchedule, cmacState->iv.t.buffer, cmacState->iv.t.buffer); cmacState->bcount = 0; } for(;(size > 0) && (cmacState->bcount < cmacState->iv.t.size); size--, cmacState->bcount++) { cmacState->iv.t.buffer[cmacState->bcount] ^= *buffer++; } } } /* 10.2.6.3.3 CryptCmacEnd() */ /* This is the completion function for the CMAC. It does padding, if needed, and selects the subkey to be applied before the last block is encrypted. */ UINT16 CryptCmacEnd( SMAC_STATES *state, UINT32 outSize, BYTE *outBuffer ) { tpmCmacState_t *cState = &state->cmac; // Need to set algorithm, key, and keySizeInBits in the local context so that // the SELECT and ENCRYPT macros will work here TPM_ALG_ID algorithm = cState->symAlg; BYTE *key = cState->symKey.t.buffer; UINT16 keySizeInBits = cState->keySizeBits; tpmCryptKeySchedule_t keySchedule; TpmCryptSetSymKeyCall_t encrypt; TPM2B_IV subkey = {{0, {0}}}; BOOL xorVal; UINT16 i; subkey.t.size = cState->iv.t.size; // Encrypt a block of zero // Set up the encryption values based on the algorithm switch (algorithm) { FOR_EACH_SYM(ENCRYPT_CASE) default: return 0; } ENCRYPT(&keySchedule, subkey.t.buffer, subkey.t.buffer); // shift left by 1 and XOR with 0x0...87 if the MSb was 0 xorVal = ((subkey.t.buffer[0] & 0x80) == 0) ? 0 : 0x87; ShiftLeft(&subkey.b); subkey.t.buffer[subkey.t.size - 1] ^= xorVal; // this is a sanity check to make sure that the algorithm is working properly. // remove this check when debug is done pAssert(cState->bcount <= cState->iv.t.size); // If the buffer is full then no need to compute subkey 2. if(cState->bcount < cState->iv.t.size) { //Pad the data cState->iv.t.buffer[cState->bcount++] ^= 0x80; // The rest of the data is a pad of zero which would simply be XORed // with the iv value so nothing to do... // Now compute K2 xorVal = ((subkey.t.buffer[0] & 0x80) == 0) ? 0 : 0x87; ShiftLeft(&subkey.b); subkey.t.buffer[subkey.t.size - 1] ^= xorVal; } // XOR the subkey into the IV for(i = 0; i < subkey.t.size; i++) cState->iv.t.buffer[i] ^= subkey.t.buffer[i]; ENCRYPT(&keySchedule, cState->iv.t.buffer, cState->iv.t.buffer); i = (UINT16)MIN(cState->iv.t.size, outSize); MemoryCopy(outBuffer, cState->iv.t.buffer, i); return i; } #endif