Getting jargon before actual data when printing char pointer - c

Question

I'm writing a program that implements the Alberti Cipher, and when testing, the final print always gives a string of jargon before the actual encryption. Right now its printing \x80\x16G\xbf\xfe\x7fKHOORZRUOG, with KHOOR..... being the actual encryption. Any help appreciated :)
#include <stdio.h>
#include <stdlib.h>
int letterToNumber(char letter){
char str[2] = { letter };
int num = strtol( str, NULL, 36 ) - 10;
return num;
}
int getSize (const char * s) {
const char * t;
int size = 0;
for (t = s; *t != '\0'; t++) {
size++;
}
return size;
}
char numToChar(int numInp){
numInp=numInp+65;
char returnChar=(char)numInp;
return returnChar;
}
void encrypt_alberti(const char *message,const char *inner_ring, int initialShift,int periodicShift,int periodLength,char **result){
//sets initial shift
int numArray[25];
int count=0;
int shiftCount=0;
for(int i = 0; i < 26; ++i) {
numArray[i]=(i+initialShift)%26;
}
//encrypts each character and prints
int messageSize=getSize(message);
char encryptedMessage[messageSize];
for(int i=0; i<messageSize;i++){
count++;
if(periodicShift!=0){
if(count%periodicShift==0){
shiftCount++;
}
}
else{
periodLength=0;
}
char toBeEncrypted=message[i];
int charNumber=letterToNumber(toBeEncrypted);
int encryptedNum=numArray[(charNumber+(shiftCount*periodLength))%26];
char encryptedChar=numToChar(encryptedNum);
strncat(encryptedMessage, &encryptedChar, 1);
}
char* p1=malloc(sizeof(encryptedMessage));
strcpy(p1,encryptedMessage);
*result=p1;
}
void main(void) {
const char *example_message = "HELLOWORLD";
const char *example_inner = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char *encrypted_message = NULL;
encrypt_alberti(example_message, example_inner, 3, 0, 1, &encrypted_message);
printf("message is %s\n", encrypted_message);
printf("-----------------");
free(encrypted_message);
}
}