System Security : C code for Vigenere Cipher (should be executed in linux with gcc).

//Aim:To implement vigenere cipher in C. //Program: #include<stdio.h> void main() { int i; int kl; int pl; printf("Enter the length of the key stream. "); scanf("%d",&kl); printf("Enter the length of the plain text stream.(Without spaces) "); scanf("%d",&pl); char p[pl]; char k[kl]; printf("\nEnter the Key. "); for(i=-1;i<kl;++i) scanf("%c",&k[i]); printf("\nEnter the Plain text. "); for(i=-1;i<pl;++i) scanf("%c",&p[i]); int s[3][pl]; for(i=0;i<pl;++i) { if(65<=p[i] && p[i]<=91) s[0][i]=p[i]%65; else s[0][i]=p[i]%97; } for(i=0;i<pl;++i) printf("%d ",s[0][i]); int count=0; while(count<pl) { for(i=0;i<kl;++i) { if(65<=k[i] && k[i]<=91) s[1][count+i]=k[i]%65; else s[1][count+i]=k[i]%97; } count=count+kl; } printf("\n"); for(i=0;i<pl;++i) printf("%d ",s[1][i]); printf("\n"); for(i=0;i<pl;++i) printf("%d ",s[2][i]); printf("\n\nThe cipher text is: "); char cipher[kl]; for(i=0;i<pl;++i) { s[2][i]=(s[0][i]+s[1][i])%26; cipher[i]=(char)(s[2][i]+65); printf("%c ",cipher[i]); } } /*Output lab2@lab2-OptiPlex-330:~/Desktop$ gcc vigenere.c lab2@lab2-OptiPlex-330:~/Desktop$ ./a.out Enter the length of the key stream. 6 Enter the length of the plain text stream.(Without spaces) 14 Enter the Key. pascal Enter the Plain text. sheislistening 18 7 4 8 18 11 8 18 19 4 13 8 13 6 15 0 18 2 0 11 15 0 18 2 0 11 15 0 The cipher text is: H H W K S W X S L G N T C G */

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