diff --git a/src/ltc/encauth/ccm/ccm_init.c b/src/ltc/encauth/ccm/ccm_init.c
index 20c2a17..b1bd12d 100644
--- a/src/ltc/encauth/ccm/ccm_init.c
+++ b/src/ltc/encauth/ccm/ccm_init.c
@@ -29,7 +29,6 @@
 
    LTC_ARGCHK(ccm    != NULL);
    LTC_ARGCHK(key    != NULL);
-   LTC_ARGCHK(taglen != 0);
 
    XMEMSET(ccm, 0, sizeof(ccm_state));
 
@@ -41,17 +40,11 @@
       return CRYPT_INVALID_CIPHER;
    }
 
-   /* make sure the taglen is even and <= 16 */
-   ccm->taglen = taglen;
-   ccm->taglen &= ~1;
-   if (ccm->taglen > 16) {
-      ccm->taglen = 16;
-   }
-
-   /* can't use < 4 */
-   if (ccm->taglen < 4) {
+   /* make sure the taglen is valid */
+   if (taglen < 4 || taglen > 16 || (taglen % 2) == 1) {
       return CRYPT_INVALID_ARG;
    }
+   ccm->taglen = taglen;
 
    /* schedule key */
    if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &ccm->K)) != CRYPT_OK) {
diff --git a/src/ltc/encauth/ccm/ccm_memory.c b/src/ltc/encauth/ccm/ccm_memory.c
index 40ecba6..7280133 100644
--- a/src/ltc/encauth/ccm/ccm_memory.c
+++ b/src/ltc/encauth/ccm/ccm_memory.c
@@ -80,14 +80,8 @@
       return CRYPT_INVALID_CIPHER;
    }
 
-   /* make sure the taglen is even and <= 16 */
-   *taglen &= ~1;
-   if (*taglen > 16) {
-      *taglen = 16;
-   }
-
-   /* can't use < 4 */
-   if (*taglen < 4) {
+   /* make sure the taglen is valid */
+   if (*taglen < 4 || *taglen > 16 || (*taglen % 2) == 1) {
       return CRYPT_INVALID_ARG;
    }
 
diff --git a/src/ltc/encauth/chachapoly/chacha20poly1305_decrypt.c b/src/ltc/encauth/chachapoly/chacha20poly1305_decrypt.c
index f19cf18..493404f 100644
--- a/src/ltc/encauth/chachapoly/chacha20poly1305_decrypt.c
+++ b/src/ltc/encauth/chachapoly/chacha20poly1305_decrypt.c
@@ -25,7 +25,6 @@
    unsigned long padlen;
    int err;
 
-   if (inlen == 0) return CRYPT_OK; /* nothing to do */
    LTC_ARGCHK(st != NULL);
 
    if (st->aadflg) {
diff --git a/src/ltc/encauth/chachapoly/chacha20poly1305_encrypt.c b/src/ltc/encauth/chachapoly/chacha20poly1305_encrypt.c
index aeecc18..04c5515 100644
--- a/src/ltc/encauth/chachapoly/chacha20poly1305_encrypt.c
+++ b/src/ltc/encauth/chachapoly/chacha20poly1305_encrypt.c
@@ -25,7 +25,6 @@
    unsigned long padlen;
    int err;
 
-   if (inlen == 0) return CRYPT_OK; /* nothing to do */
    LTC_ARGCHK(st != NULL);
 
    if ((err = chacha_crypt(&st->chacha, in, inlen, out)) != CRYPT_OK)         return err;
diff --git a/src/ltc/encauth/chachapoly/chacha20poly1305_memory.c b/src/ltc/encauth/chachapoly/chacha20poly1305_memory.c
index 34da912..ddd0517 100644
--- a/src/ltc/encauth/chachapoly/chacha20poly1305_memory.c
+++ b/src/ltc/encauth/chachapoly/chacha20poly1305_memory.c
@@ -43,6 +43,7 @@
    LTC_ARGCHK(in  != NULL);
    LTC_ARGCHK(out != NULL);
    LTC_ARGCHK(tag != NULL);
+   LTC_ARGCHK(taglen != NULL);
 
    if ((err = chacha20poly1305_init(&st, key, keylen)) != CRYPT_OK)          { goto LBL_ERR; }
    if ((err = chacha20poly1305_setiv(&st, iv, ivlen)) != CRYPT_OK)           { goto LBL_ERR; }
@@ -51,15 +52,22 @@
    }
    if (direction == CHACHA20POLY1305_ENCRYPT) {
       if ((err = chacha20poly1305_encrypt(&st, in, inlen, out)) != CRYPT_OK) { goto LBL_ERR; }
+      if ((err = chacha20poly1305_done(&st, tag, taglen)) != CRYPT_OK)       { goto LBL_ERR; }
    }
    else if (direction == CHACHA20POLY1305_DECRYPT) {
+      unsigned char buf[MAXBLOCKSIZE];
+      unsigned long buflen = sizeof(buf);
       if ((err = chacha20poly1305_decrypt(&st, in, inlen, out)) != CRYPT_OK) { goto LBL_ERR; }
+      if ((err = chacha20poly1305_done(&st, buf, &buflen)) != CRYPT_OK)      { goto LBL_ERR; }
+      if (buflen != *taglen || XMEM_NEQ(buf, tag, buflen) != 0) {
+         err = CRYPT_ERROR;
+         goto LBL_ERR;
+      }
    }
    else {
       err = CRYPT_INVALID_ARG;
       goto LBL_ERR;
    }
-   err = chacha20poly1305_done(&st, tag, taglen);
 LBL_ERR:
 #ifdef LTC_CLEAN_STACK
    zeromem(&st, sizeof(chacha20poly1305_state));
diff --git a/src/ltc/encauth/gcm/gcm_memory.c b/src/ltc/encauth/gcm/gcm_memory.c
index b318f7c..a9c6ac6 100644
--- a/src/ltc/encauth/gcm/gcm_memory.c
+++ b/src/ltc/encauth/gcm/gcm_memory.c
@@ -93,7 +93,24 @@
     if ((err = gcm_process(gcm, pt, ptlen, ct, direction)) != CRYPT_OK) {
        goto LTC_ERR;
     }
-    err = gcm_done(gcm, tag, taglen);
+    if (direction == GCM_ENCRYPT) {
+      if ((err = gcm_done(gcm, tag, taglen)) != CRYPT_OK) {
+         goto LTC_ERR;
+      }
+    }
+    else if (direction == GCM_DECRYPT) {
+       unsigned char buf[MAXBLOCKSIZE];
+       unsigned long buflen = sizeof(buf);
+       if ((err = gcm_done(gcm, buf, &buflen)) != CRYPT_OK) {
+          goto LTC_ERR;
+       }
+       if (buflen != *taglen || XMEM_NEQ(buf, tag, buflen) != 0) {
+          err = CRYPT_ERROR;
+       }
+    }
+    else {
+       err = CRYPT_INVALID_ARG;
+    }
 LTC_ERR:
     XFREE(orig);
     return err;
diff --git a/src/ltc/misc/copy_or_zeromem.c b/src/ltc/misc/copy_or_zeromem.c
index 1cfd2bd..447b268 100644
--- a/src/ltc/misc/copy_or_zeromem.c
+++ b/src/ltc/misc/copy_or_zeromem.c
@@ -29,8 +29,7 @@
 #endif
    unsigned char mask = 0xff; /* initialize mask at all ones */
 
-   LTC_ARGCHK(src  != NULL);
-   LTC_ARGCHK(dest != NULL);
+   if (src == NULL || dest == NULL) return;
 
    if (coz != 0) coz = 1;
    y = 0;