diff --git a/README.md b/README.md
new file mode 100644
index 0000000..6e3fcaa
--- /dev/null
+++ b/README.md
@@ -0,0 +1,26 @@
+<h1 align="center">PKCS7-Padding</h1>
+
+Implementation of PKCS7 padding in C. It can be used to pre-prepare data before block cipher using (for example, AES).
+
+# Algorithm description
+
+   PKCS7 is described in [RFC 5652](https://tools.ietf.org/html/rfc5652#section-6.3).
+    
+   Some content-encryption algorithms assume the input length is a
+   multiple of k octets, where k is greater than one.  For such
+   algorithms, the input shall be padded at the trailing end with
+   k-(lth mod k) octets all having value k-(lth mod k), where lth is
+   the length of the input.  In other words, the input is padded at
+   the trailing end with one of the following strings:
+
+                     01 -- if lth mod k = k-1
+                  02 02 -- if lth mod k = k-2
+                      .
+                      .
+                      .
+            k k ... k k -- if lth mod k = 0
+
+   The padding can be removed unambiguously since all input is padded,
+   including input values that are already a multiple of the block size,
+   and no padding string is a suffix of another.  This padding method is
+   well defined if and only if k is less than 256.