diff --git a/crypto/cipher/e_chacha20poly1305.c b/crypto/cipher/e_chacha20poly1305.c
index 34446b4..29ada9b 100644
--- a/crypto/cipher/e_chacha20poly1305.c
+++ b/crypto/cipher/e_chacha20poly1305.c
@@ -67,18 +67,15 @@
   OPENSSL_free(c20_ctx);
 }
 
-static void poly1305_update_with_length(poly1305_state *poly1305,
-                                        const uint8_t *data, size_t data_len) {
-  size_t j = data_len;
+static void poly1305_update_length(poly1305_state *poly1305, size_t data_len) {
   uint8_t length_bytes[8];
   unsigned i;
 
   for (i = 0; i < sizeof(length_bytes); i++) {
-    length_bytes[i] = j;
-    j >>= 8;
+    length_bytes[i] = data_len;
+    data_len >>= 8;
   }
 
-  CRYPTO_poly1305_update(poly1305, data, data_len);
   CRYPTO_poly1305_update(poly1305, length_bytes, sizeof(length_bytes));
 }
 
@@ -88,14 +85,34 @@
 #define ALIGNED
 #endif
 
-static int aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, uint8_t *out,
-                                       size_t *out_len, size_t max_out_len,
-                                       const uint8_t *nonce, size_t nonce_len,
-                                       const uint8_t *in, size_t in_len,
-                                       const uint8_t *ad, size_t ad_len) {
-  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
+typedef void (*aead_poly1305_update)(poly1305_state *ctx, const uint8_t *ad,
+                                     size_t ad_len, const uint8_t *ciphertext,
+                                     size_t ciphertext_len);
+
+/* aead_poly1305 fills |tag| with the authentication tag for the given
+ * inputs, using |update| to control the order and format that the inputs are
+ * signed/authenticated. */
+static void aead_poly1305(aead_poly1305_update update,
+                          uint8_t tag[POLY1305_TAG_LEN],
+                          const struct aead_chacha20_poly1305_ctx *c20_ctx,
+                          const uint8_t nonce[12], const uint8_t *ad,
+                          size_t ad_len, const uint8_t *ciphertext,
+                          size_t ciphertext_len) {
   uint8_t poly1305_key[32] ALIGNED;
-  poly1305_state poly1305;
+  memset(poly1305_key, 0, sizeof(poly1305_key));
+  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
+                   c20_ctx->key, nonce, 0);
+  poly1305_state ctx;
+  CRYPTO_poly1305_init(&ctx, poly1305_key);
+  update(&ctx, ad, ad_len, ciphertext, ciphertext_len);
+  CRYPTO_poly1305_finish(&ctx, tag);
+}
+
+static int seal(aead_poly1305_update poly1305_update, const EVP_AEAD_CTX *ctx,
+                uint8_t *out, size_t *out_len, size_t max_out_len,
+                const uint8_t nonce[12], const uint8_t *in, size_t in_len,
+                const uint8_t *ad, size_t ad_len) {
+  const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
   const uint64_t in_len_64 = in_len;
 
   /* |CRYPTO_chacha_20| uses a 32-bit block counter. Therefore we disallow
@@ -119,40 +136,22 @@
     return 0;
   }
 
-  if (nonce_len != 8) {
-    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_IV_TOO_LARGE);
-    return 0;
-  }
-  uint8_t nonce_96[12];
-  memset(nonce_96, 0, 4);
-  memcpy(nonce_96 + 4, nonce, 8);
-
-  memset(poly1305_key, 0, sizeof(poly1305_key));
-  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
-                   c20_ctx->key, nonce_96, 0);
-
-  CRYPTO_poly1305_init(&poly1305, poly1305_key);
-  poly1305_update_with_length(&poly1305, ad, ad_len);
-  CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce_96, 1);
-  poly1305_update_with_length(&poly1305, out, in_len);
+  CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
 
   uint8_t tag[POLY1305_TAG_LEN] ALIGNED;
-  CRYPTO_poly1305_finish(&poly1305, tag);
+  aead_poly1305(poly1305_update, tag, c20_ctx, nonce, ad, ad_len, out, in_len);
+
   memcpy(out + in_len, tag, c20_ctx->tag_len);
   *out_len = in_len + c20_ctx->tag_len;
   return 1;
 }
 
-static int aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, uint8_t *out,
-                                       size_t *out_len, size_t max_out_len,
-                                       const uint8_t *nonce, size_t nonce_len,
-                                       const uint8_t *in, size_t in_len,
-                                       const uint8_t *ad, size_t ad_len) {
+static int open(aead_poly1305_update poly1305_update, const EVP_AEAD_CTX *ctx,
+                uint8_t *out, size_t *out_len, size_t max_out_len,
+                const uint8_t nonce[12], const uint8_t *in, size_t in_len,
+                const uint8_t *ad, size_t ad_len) {
   const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
-  uint8_t mac[POLY1305_TAG_LEN];
-  uint8_t poly1305_key[32] ALIGNED;
   size_t plaintext_len;
-  poly1305_state poly1305;
   const uint64_t in_len_64 = in_len;
 
   if (in_len < c20_ctx->tag_len) {
@@ -171,43 +170,68 @@
     return 0;
   }
 
-  if (nonce_len != 8) {
-    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_IV_TOO_LARGE);
-    return 0;
-  }
-  uint8_t nonce_96[12];
-  memset(nonce_96, 0, 4);
-  memcpy(nonce_96 + 4, nonce, 8);
-
   plaintext_len = in_len - c20_ctx->tag_len;
-
-  if (max_out_len < plaintext_len) {
-    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
-    return 0;
-  }
-
-  memset(poly1305_key, 0, sizeof(poly1305_key));
-  CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
-                   c20_ctx->key, nonce_96, 0);
-
-  CRYPTO_poly1305_init(&poly1305, poly1305_key);
-  poly1305_update_with_length(&poly1305, ad, ad_len);
-  poly1305_update_with_length(&poly1305, in, plaintext_len);
-  CRYPTO_poly1305_finish(&poly1305, mac);
-
-  if (CRYPTO_memcmp(mac, in + plaintext_len, c20_ctx->tag_len) != 0) {
+  uint8_t tag[POLY1305_TAG_LEN] ALIGNED;
+  aead_poly1305(poly1305_update, tag, c20_ctx, nonce, ad, ad_len, in,
+                plaintext_len);
+  if (CRYPTO_memcmp(tag, in + plaintext_len, c20_ctx->tag_len) != 0) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
     return 0;
   }
 
-  CRYPTO_chacha_20(out, in, plaintext_len, c20_ctx->key, nonce_96, 1);
+  CRYPTO_chacha_20(out, in, plaintext_len, c20_ctx->key, nonce, 1);
   *out_len = plaintext_len;
   return 1;
 }
 
+static void poly1305_update_padded_16(poly1305_state *poly1305,
+                                      const uint8_t *data, size_t data_len) {
+  static const uint8_t padding[16] = { 0 }; /* Padding is all zeros. */
+
+  CRYPTO_poly1305_update(poly1305, data, data_len);
+  if (data_len % 16 != 0) {
+    CRYPTO_poly1305_update(poly1305, padding, sizeof(padding) - (data_len % 16));
+  }
+}
+
+static void poly1305_update(poly1305_state *ctx, const uint8_t *ad,
+                            size_t ad_len, const uint8_t *ciphertext,
+                            size_t ciphertext_len) {
+  poly1305_update_padded_16(ctx, ad, ad_len);
+  poly1305_update_padded_16(ctx, ciphertext, ciphertext_len);
+  poly1305_update_length(ctx, ad_len);
+  poly1305_update_length(ctx, ciphertext_len);
+}
+
+static int aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, uint8_t *out,
+                                       size_t *out_len, size_t max_out_len,
+                                       const uint8_t *nonce, size_t nonce_len,
+                                       const uint8_t *in, size_t in_len,
+                                       const uint8_t *ad, size_t ad_len) {
+  if (nonce_len != 12) {
+    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
+    return 0;
+  }
+  return seal(poly1305_update, ctx, out, out_len, max_out_len, nonce, in,
+              in_len, ad, ad_len);
+}
+
+static int aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, uint8_t *out,
+                                       size_t *out_len, size_t max_out_len,
+                                       const uint8_t *nonce, size_t nonce_len,
+                                       const uint8_t *in, size_t in_len,
+                                       const uint8_t *ad, size_t ad_len) {
+  if (nonce_len != 12) {
+    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
+    return 0;
+  }
+  return open(poly1305_update, ctx, out, out_len, max_out_len, nonce, in,
+              in_len, ad, ad_len);
+}
+
 static const EVP_AEAD aead_chacha20_poly1305 = {
     32,                 /* key len */
-    8,                  /* nonce len */
+    12,                 /* nonce len */
     POLY1305_TAG_LEN,   /* overhead */
     POLY1305_TAG_LEN,   /* max tag length */
     aead_chacha20_poly1305_init,
@@ -221,3 +245,59 @@
 const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
   return &aead_chacha20_poly1305;
 }
+
+static void poly1305_update_old(poly1305_state *ctx, const uint8_t *ad,
+                                size_t ad_len, const uint8_t *ciphertext,
+                                size_t ciphertext_len) {
+  CRYPTO_poly1305_update(ctx, ad, ad_len);
+  poly1305_update_length(ctx, ad_len);
+  CRYPTO_poly1305_update(ctx, ciphertext, ciphertext_len);
+  poly1305_update_length(ctx, ciphertext_len);
+}
+
+static int aead_chacha20_poly1305_old_seal(
+    const EVP_AEAD_CTX *ctx, uint8_t *out, size_t *out_len, size_t max_out_len,
+    const uint8_t *nonce, size_t nonce_len, const uint8_t *in, size_t in_len,
+    const uint8_t *ad, size_t ad_len) {
+  if (nonce_len != 8) {
+    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
+    return 0;
+  }
+  uint8_t nonce_96[12];
+  memset(nonce_96, 0, 4);
+  memcpy(nonce_96 + 4, nonce, 8);
+  return seal(poly1305_update_old, ctx, out, out_len, max_out_len, nonce_96, in,
+              in_len, ad, ad_len);
+}
+
+static int aead_chacha20_poly1305_old_open(
+    const EVP_AEAD_CTX *ctx, uint8_t *out, size_t *out_len, size_t max_out_len,
+    const uint8_t *nonce, size_t nonce_len, const uint8_t *in, size_t in_len,
+    const uint8_t *ad, size_t ad_len) {
+  if (nonce_len != 8) {
+    OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
+    return 0;
+  }
+  uint8_t nonce_96[12];
+  memset(nonce_96, 0, 4);
+  memcpy(nonce_96 + 4, nonce, 8);
+  return open(poly1305_update_old, ctx, out, out_len, max_out_len, nonce_96, in,
+              in_len, ad, ad_len);
+}
+
+static const EVP_AEAD aead_chacha20_poly1305_old = {
+    32,                 /* key len */
+    8,                  /* nonce len */
+    POLY1305_TAG_LEN,   /* overhead */
+    POLY1305_TAG_LEN,   /* max tag length */
+    aead_chacha20_poly1305_init,
+    NULL, /* init_with_direction */
+    aead_chacha20_poly1305_cleanup,
+    aead_chacha20_poly1305_old_seal,
+    aead_chacha20_poly1305_old_open,
+    NULL,               /* get_rc4_state */
+};
+
+const EVP_AEAD *EVP_aead_chacha20_poly1305_old(void) {
+  return &aead_chacha20_poly1305_old;
+}