diff --git a/README.md b/README.md
index bf83831..d687c01 100644
--- a/README.md
+++ b/README.md
@@ -20,9 +20,9 @@ const options = {
   curveName: 'secp256k1',
   symmetricCypherName: 'aes-128-ecb',
   iv: null,
-  // iv is used in symmetric cipher, set null if you want to use cipher
-  // in ecb mode. set undefined if you want to use deprecated
-  // createCipheriv / createDecipher / EVP_BytesToKey
+  // iv is used in symmetric cipher, set null if the cipher does not need an
+  // initialization vector (e.g. a cipher in ecb mode). Set undefined if you
+  // want to use deprecated createCipheriv / createDecipher / EVP_BytesToKey
   keyFormat: 'uncompressed',
   s1: null, // optional shared information1
   s2: null // optional shared information2
@@ -35,3 +35,8 @@ const encryptedText = ecies.encrypt(ecdh.getPublicKey(), plainText, options);
 const decryptedText = ecies.decrypt(ecdh, encryptedText, options);
 assert(plainText.toString('hex') == decryptedText.toString('hex'));
 ```
+
+## Porting from 1.0.0 to 2.0.0
+For the projects used this library with options.iv set to a valid iv buffer, no change is required to make compatible with 1.0.0. Other projects can set `options.iv = undefined` to make compatible with an older version.
+
+In the version 1.0.0, it is advised to use a null iv for ECB mode ciphers, which will use crypto.createCipher -> EVP_BytesToKey to derive a key. However, as noted in [the latest manual of EVP_BytesToKey](https://www.openssl.org/docs/man1.1.0/man3/EVP_BytesToKey.html) that "Newer applications should use a more modern algorithm such as PBKDF2 as defined in PKCS#5v2.1 and provided by PKCS5_PBKDF2_HMAC", crypto.createCipher is deprecated by nodejs. Therefore, to avoid this library to use deprecated nodejs API by default, the behavior of `options.iv == null` now is to use crypto.createCipheriv with an empty iv to create the cipher which, however, is incompatible with the cipher created by crypto.createCipher.
diff --git a/package.json b/package.json
index a6d84c2..825e1ee 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "standard-ecies",
-  "version": "1.0.0",
+  "version": "2.0.0",
   "description": "Standard ECIES implemention for NodeJS based on crypto module with no other dependencies.",
   "main": "main.js",
   "scripts": {