Hill Cipher - Program in C

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int **matrixMultiply(int**a,int r1,int c1,int **b,int r2,int c2)
{
 int **resultMatrix;
 int i,j,k,r,c;
 r=r1;c=c2;
 resultMatrix=(int**)malloc(sizeof(int*)*r);
 for(i=0;i<r;i++)
  resultMatrix[i]=(int*)malloc(sizeof(int)*c);
 for(i=0;i<r;i++)
 {
  for(j=0;j<c;j++)
  {
   resultMatrix[i][j]=0;
   for(k=0;k<c1;k++)
    resultMatrix[i][j]+=a[i][k]*b[k][j];
  }
 }
 return resultMatrix;
}
void printMatrix(int**matrix,int r,int c)
{
 int i,j;
 for(i=0;i<r;i++)
 {
  for(j=0;j<c;j++)
   printf("%d ",matrix[i][j]);
  printf("\n");
 }
}
int plainTextToCipherText(char plainText[],int**matrix)
{
 int len,**plainTextMatrix,**resultMatrix,i,j;
 // The matrix will be of dimensions strlen(plainText) by strlen(plainText)
 char *cipherText;
 len=strlen(plainText);
 cipherText=(char*)malloc(sizeof(char)*1000);

 // plainTextMatrix should be of dimension strlen(plainText) by 1
 // allcating memory to plainTextMatrix
 plainTextMatrix=(int**)malloc(sizeof(int*)*len);
 for(i=0;i<len;i++)
  plainTextMatrix[i]=(int*)malloc(sizeof(int)*1);

 // populating the plainTextMatrix
 for(i=0;i<len;i++)
  for(j=0;j<1;j++)
   plainTextMatrix[i][j]=plainText[i]-'a';

 resultMatrix=matrixMultiply(matrix,len,len,plainTextMatrix,len,1);
 
 // taking mod 26 of each element of the result matrix
 for(i=0;i<len;i++)
  for(j=0;j<1;j++)
   resultMatrix[i][j]%=26;

 // Printing the cipher text
 printf("The cipher text is as follows : ");
 for(i=0;i<len;i++)
  for(j=0;j<1;j++)
   printf("%c",resultMatrix[i][j]+'a');
 printf("\n");
 //printMatrix(resultMatrix,len,1);
}
int main()
{
 int len,i,j,**matrix;
 char plainText[1000];
 printf("Enter the word to be encrypted : ");
 scanf(" %s",plainText);
 len=strlen(plainText);

 // allocating memory to matrix
 matrix=(int**)malloc(sizeof(int*)*len);
 for(i=0;i<len;i++)
  matrix[i]=(int*)malloc(sizeof(int)*len);

 printf("Enter the matrix of %d by %d to be used in encryption process : \n",len,len);
 for(i=0;i<len;i++)
  for(j=0;j<len;j++)
   scanf("%d",&matrix[i][j]);

 plainTextToCipherText(plainText,matrix);
 return 0;
}