diff --git a/inc/CryptX_AuthEnc_ChaCha20Poly1305.xs.inc b/inc/CryptX_AuthEnc_ChaCha20Poly1305.xs.inc
index e5b32d0..42df04d 100644
--- a/inc/CryptX_AuthEnc_ChaCha20Poly1305.xs.inc
+++ b/inc/CryptX_AuthEnc_ChaCha20Poly1305.xs.inc
@@ -36,6 +36,18 @@
         Newz(0, RETVAL, 1, struct chacha20poly1305_struct);
         if (!RETVAL) croak("FATAL: Newz failed");
         Copy(&self->state, &RETVAL->state, 1, struct chacha20poly1305_struct);
+    OUTPUT:
+        RETVAL
+
+int
+increment_iv(Crypt::AuthEnc::ChaCha20Poly1305 self)
+    CODE:
+    {
+        int rv;
+        rv = chacha20poly1305_inciv(&self->state);
+        if (rv != CRYPT_OK) croak("FATAL: chacha20poly1305_inciv failed: %s", error_to_string(rv));
+        RETVAL = rv;
+    }
     OUTPUT:
         RETVAL
 
diff --git a/lib/Crypt/AuthEnc/ChaCha20Poly1305.pm b/lib/Crypt/AuthEnc/ChaCha20Poly1305.pm
index 4cf29d3..b7b483b 100644
--- a/lib/Crypt/AuthEnc/ChaCha20Poly1305.pm
+++ b/lib/Crypt/AuthEnc/ChaCha20Poly1305.pm
@@ -82,7 +82,7 @@
 
 =head1 DESCRIPTION
 
-Galois/Counter Mode (ChaCha20Poly1305) - provides encryption and authentication.
+Provides encryption and authentication based on ChaCha20 + Poly1305 as defined in RFC 7539 - L<https://tools.ietf.org/html/rfc7539>
 
 =head1 EXPORT
 
@@ -145,6 +145,10 @@
 
  my $ae_new = $ae->clone;
 
+=head2 increment_iv
+
+ $ae->increment_iv;
+
 =head1 SEE ALSO
 
 =over
diff --git a/src/Makefile b/src/Makefile
index 3015d00..2c017bb 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -9,6 +9,7 @@
 ltc/encauth/chachapoly/chacha20poly1305_done.o ltc/encauth/chachapoly/chacha20poly1305_encrypt.o \
 ltc/encauth/chachapoly/chacha20poly1305_init.o ltc/encauth/chachapoly/chacha20poly1305_memory.o \
 ltc/encauth/chachapoly/chacha20poly1305_setiv.o ltc/encauth/chachapoly/chacha20poly1305_setiv_rfc7905.o \
+ltc/encauth/chachapoly/chacha20poly1305_inciv.o \
 ltc/encauth/ccm/ccm_add_aad.o ltc/encauth/ccm/ccm_add_nonce.o ltc/encauth/ccm/ccm_done.o ltc/encauth/ccm/ccm_init.o \
 ltc/encauth/ccm/ccm_memory.o ltc/encauth/ccm/ccm_process.o ltc/encauth/ccm/ccm_reset.o \
 ltc/encauth/eax/eax_addheader.o ltc/encauth/eax/eax_decrypt.o ltc/encauth/eax/eax_decrypt_verify_memory.o \
diff --git a/src/Makefile.nmake b/src/Makefile.nmake
index 01003f4..4cd43d6 100644
--- a/src/Makefile.nmake
+++ b/src/Makefile.nmake
@@ -9,6 +9,7 @@
 ltc/encauth/chachapoly/chacha20poly1305_done.obj ltc/encauth/chachapoly/chacha20poly1305_encrypt.obj \
 ltc/encauth/chachapoly/chacha20poly1305_init.obj ltc/encauth/chachapoly/chacha20poly1305_memory.obj \
 ltc/encauth/chachapoly/chacha20poly1305_setiv.obj ltc/encauth/chachapoly/chacha20poly1305_setiv_rfc7905.obj \
+ltc/encauth/chachapoly/chacha20poly1305_inciv.obj \
 ltc/encauth/ccm/ccm_add_aad.obj ltc/encauth/ccm/ccm_add_nonce.obj ltc/encauth/ccm/ccm_done.obj ltc/encauth/ccm/ccm_init.obj \
 ltc/encauth/ccm/ccm_memory.obj ltc/encauth/ccm/ccm_process.obj ltc/encauth/ccm/ccm_reset.obj \
 ltc/encauth/eax/eax_addheader.obj ltc/encauth/eax/eax_decrypt.obj ltc/encauth/eax/eax_decrypt_verify_memory.obj \
diff --git a/src/ltc/encauth/chachapoly/chacha20poly1305_inciv.c b/src/ltc/encauth/chachapoly/chacha20poly1305_inciv.c
new file mode 100644
index 0000000..f7f3143
--- /dev/null
+++ b/src/ltc/encauth/chachapoly/chacha20poly1305_inciv.c
@@ -0,0 +1,65 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ */
+
+#include "tomcrypt.h"
+
+#ifdef LTC_CHACHA20POLY1305_MODE
+
+/**
+  Reset ChaCha20Poly1305 state with incremented IV - used by https://shadowsocks.org/en/spec/AEAD-Ciphers.html
+  @param st     The ChaCha20Poly1305 state
+  @param iv     The IV data to add
+  @param inlen  The length of the IV (must be 12 or 8)
+  @return CRYPT_OK on success
+ */
+int chacha20poly1305_inciv(chacha20poly1305_state *st)
+{
+   int err;
+   unsigned char tmp_iv[12];
+   unsigned long ivlen;
+
+   LTC_ARGCHK(st != NULL);
+
+   ivlen = st->chacha.ivlen;
+   if (ivlen == 12) {
+      STORE32L(st->chacha.input[13], tmp_iv + 0);
+      STORE32L(st->chacha.input[14], tmp_iv + 4);
+      STORE32L(st->chacha.input[15], tmp_iv + 8);
+      /* increment IV 96bit / 12 bytes */
+      if (!++tmp_iv[0] && !++tmp_iv[1] && !++tmp_iv[2]  && !++tmp_iv[3] &&
+          !++tmp_iv[4] && !++tmp_iv[5] && !++tmp_iv[6]  && !++tmp_iv[7] &&
+          !++tmp_iv[8] && !++tmp_iv[9] && !++tmp_iv[10] && !++tmp_iv[11])
+      {
+         err = CRYPT_ERROR; /* IV overflow */
+      }
+      else {
+         err = chacha20poly1305_setiv(st, tmp_iv, 12);
+      }
+   }
+   else if (ivlen == 8) {
+      STORE32L(st->chacha.input[14], tmp_iv + 0);
+      STORE32L(st->chacha.input[15], tmp_iv + 4);
+      /* increment IV 64bit / 8 bytes */
+      if (!++tmp_iv[0] && !++tmp_iv[1] && !++tmp_iv[2]  && !++tmp_iv[3] &&
+          !++tmp_iv[4] && !++tmp_iv[5] && !++tmp_iv[6]  && !++tmp_iv[7])
+      {
+         err = CRYPT_ERROR; /* IV overflow */
+      }
+      else {
+         err = chacha20poly1305_setiv(st, tmp_iv, 8);
+      }
+   }
+   else {
+      err = CRYPT_ERROR; /* invalid IV length */
+   }
+
+   return err;
+}
+
+#endif
diff --git a/src/ltc/stream/chacha/chacha_ivctr32.c b/src/ltc/stream/chacha/chacha_ivctr32.c
index 64dc838..0321568 100644
--- a/src/ltc/stream/chacha/chacha_ivctr32.c
+++ b/src/ltc/stream/chacha/chacha_ivctr32.c
@@ -36,6 +36,7 @@
    LOAD32L(st->input[14], iv + 4);
    LOAD32L(st->input[15], iv + 8);
    st->ksleft = 0;
+   st->ivlen = ivlen;
    return CRYPT_OK;
 };
 
diff --git a/src/ltc/stream/chacha/chacha_ivctr64.c b/src/ltc/stream/chacha/chacha_ivctr64.c
index c2826bb..ccc3972 100644
--- a/src/ltc/stream/chacha/chacha_ivctr64.c
+++ b/src/ltc/stream/chacha/chacha_ivctr64.c
@@ -36,6 +36,7 @@
    LOAD32L(st->input[14], iv + 0);
    LOAD32L(st->input[15], iv + 4);
    st->ksleft = 0;
+   st->ivlen = ivlen;
    return CRYPT_OK;
 };