mcrypt - Problems with libmcrypt in C -

i have client server program in c encrypts/decrypts data mcrypt library. client encrypts string wants send server, send it, , after server reads, decrypts it. bellow encrypt , decrypt function:

encrypt function:

void encrypt(char *es, char *key, char *civ, size_t  length) {      mcrypt td;     int n;      td = mcrypt_module_open(mcrypt_twofish, null, mcrypt_cfb, null );     if (td == mcrypt_failed) {         log_err(log_opts, strerror(errno));         exit(1);     }     n = mcrypt_enc_get_iv_size(td);      char iv[n + 1];     strncpy(iv, civ, n);     iv[n] = '\0';      if ((mcrypt_generic_init(td, key, key_size, iv)) < 0) {         log_err(log_opts, "while trying mcrypt_generic_init.");         exit(1);     }     mcrypt_generic(td, es, length);      if (mcrypt_module_close(td) < 0) {         log_err(log_opts, "while trying close module.");         exit(1);     }  } 

decrypt function

void decrypt(char *ds, char *key, char *civ, size_t length) {     mcrypt td;     int n;      td = mcrypt_module_open(mcrypt_twofish, null, mcrypt_cfb, null );     n = mcrypt_enc_get_iv_size(td);      char iv[n + 1];     strncpy(iv, civ, n);     iv[n + 1] = '\0';      if ((mcrypt_generic_init(td, key, key_size, iv)) < 0) {         log_err(log_opts, "trying mcrypt_generic_init.");         exit(1);     }      mdecrypt_generic(td, ds, length);     if (mcrypt_module_close(td) < 0) {         log_err(log_opts, "while trying close module.");         exit(1);     }  } 

my problem:

there cases (1 10 rate) when string decrypted on server side encrypted on client side not same original. can suggest problem can come from?

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edit

the response question, can find here, issue detailed further, being pointed out code contains bug.

in decrypt function:

char iv[n + 1]; strncpy(iv, civ, n); iv[n + 1] = '\0'; 

you have off-by-one overflow in iv[n + 1] = '\0'; statement.