encrypt/sign 2048 bit RSA key using another Rsa 2048 bit Key

[Vinod Jacob]

Hi,
 I am using libgcrypt 2048 bit encryption.

what is the maximum size of the buffer that i can encrypt using 2048
bit key.is it 2048 bit ?

 I am getting incorrect values when i try to encrypt a buffer of size
more that 2048 bit

. Encryption/decryption function is successfully finishing  .But
when i tried to print the decrypted buffer , it is showing different
values. so what would i need to do, if , I want to encrypt buffer of large
size ?

 (i know we can encrypt large buffer using AES and encrypt AEs
keys using RSA ).But my requirement is to encrypt large buffer using
RSA .


Let me try to explain what i am trying to do in more detail.

 I have to encrypt/sign Rsa ( 2048 bit) keys using another Rsa  2048 bit Key

let's say Entity A there is one Rsa Keys A_pub_key & A_sec_key and say
Entity b there is one Rsa keys B_pub_key & B_sec_key

 Now i want to encrypt A_sec_key using B_pub_key. is this possible ?
how to encrypt  RSA key using another RSA key ?
 Do i need to take each mpi values and do encryption ?
is it posssible to concate each mpi value and then encrypt it?

here is the piece of the code i am using,
==============================
if(gcry_ac_open(&GcryptRsaHd, GCRY_AC_RSA, 0)!=0)
     {
        printf (" Gcrypt RSA Cipher Open : %s\n", gpg_strerror(GcryptErrVal) );
        //return RSA_CIPHER_OPEN_FAILURE ;
     }
     data = gcry_ac_key_data_get(RsaKey);
     for (i = 0; i < gcry_ac_data_length(data); i++)
     {
           gcry_ac_data_get_index(data, 0 , i, &sName[i], &mpiTemp[i]);
           printf(" MPI %s Bits : %d \n" ,sName[i]
,gcry_mpi_get_nbits(mpiTemp[i]));
 GcryptErrVal = gcry_ac_data_encrypt( GcryptRsaHd
,/*GCRY_AC_FLAG_NO_BLINDING*/0,tGcryptRsaPubKey,mpiTemp[i],&GcryptEncryptData[i]);
           if ( GcryptErrVal )
           {
                printf (" KeyEncryption : %s :%s \n",gpg_strerror(
GcryptErrVal ), gpg_strsource( GcryptErrVal ));
                gcry_ac_close(GcryptRsaHd);
                //return SECURITY_FAILURE;
           }
           else
           {
                printf("KeyEncryption : %s \n",gpg_strerror( GcryptErrVal ));
           }
    }

    printf(":::::::::::key Decryption function ::::::::::::::::::::::::\n");
    GcryptErrVal = gcry_ac_data_new( &GcryptDecryptedData);
    for (i=0 ;i<6; i++)
    {
 GcryptErrVal = gcry_ac_data_decrypt(GcryptRsaHd
,0/*GCRY_AC_FLAG_NO_BLINDING*/,tGcryptRsaSecKey
,&mpiTemp2[i],GcryptEncryptData[i]);
        if ( GcryptErrVal )
        {
          printf (" KeyDecryption : %s :%s \n",gpg_strerror(
GcryptErrVal ), gpg_strsource( GcryptErrVal ));
          //return SECURITY_FAILURE;
        }
        else
        {
          printf (" KeyDecryption : %s  \n",gpg_strerror( GcryptErrVal ));
          printf(" MPI %s Bits : %d \n" ,sName[i]
,gcry_mpi_get_nbits(mpiTemp2[i]));
          if(gcry_mpi_cmp(mpiTemp[i],mpiTemp2[i] )==0)
          {
                 printf ("MPI cmp success \n");
          }
          else
                printf ("*********MPI CMP FAILURE ***********\n");
          if (gcry_ac_data_set(GcryptDecryptedData,
GCRY_AC_FLAG_COPY,/*RsaKeyMpiNames[i]*/sName[i], mpiTemp2[i]))
          {
            gcry_ac_close(GcryptRsaHd);
            gcry_mpi_release(mpiTemp2[i]);
            //return -3;
          }
         gcry_mpi_release(mpiTemp2[i]);
       }

    }
    gcry_ac_key_init(&GcryptTestKey,GcryptRsaHd,GCRY_AC_KEY_SECRET ,
GcryptDecryptedData);
    GcryptErrVal = gcry_ac_key_test(GcryptRsaHd ,GcryptTestKey );
    if(GcryptErrVal)
    {
         printf ("********** Testing Rsa Secret Key :
%s\n",gpg_strerror(  GcryptErrVal ),gpg_strsource( GcryptErrVal ));
         gcry_ac_close(GcryptRsaHd);
         //return RSA_KEY_TEST_FAILURE;  /* TBC */
    }
    else
       printf ("************Testing Rsa Secret Key :
%s\n",gpg_strerror(  GcryptErrVal ),gpg_strsource( GcryptErrVal ));


And this is the output..
==============

 KeyEncryption : Success
 MPI e Bits : 6
 KeyEncryption : Success
 MPI d Bits : 2041
 KeyEncryption : Success
 MPI p Bits : 1024
 KeyEncryption : Success
 MPI q Bits : 1024
 KeyEncryption : Success
 MPI u Bits : 1024
 KeyEncryption : Success
 :::::::::::key Decryption function ::::::::::::::::::::::::
 KeyDecryption : Success
 MPI n Bits : 0
 *********MPI CMP FAILURE ***********
 KeyDecryption : Success
 MPI e Bits : 6
 MPI cmp success
 KeyDecryption : Success
 MPI d Bits : 2041
 MPI cmp success
 KeyDecryption : Success
 MPI p Bits : 1024
 MPI cmp success
 KeyDecryption : Success
 MPI q Bits : 1024
 MPI cmp success
 KeyDecryption : Success
 MPI u Bits : 1024
 MPI cmp success
 ********** Testing Rsa Secret Key : Invalid public key algorithm

 What is that i am missing here? could some one help me in solving this one  ?

thanks
  Vinod