docs updated

rsa/README.md

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+## RSA cryptosystem & Blind signature & Homomorphic Multiplication
+- https://en.wikipedia.org/wiki/RSA_(cryptosystem)#
+- https://en.wikipedia.org/wiki/Blind_signature
+- https://en.wikipedia.org/wiki/Homomorphic_encryption
+
+- [x] GenerateKeyPair
+- [x] Encrypt
+- [x] Decrypt
+- [x] Blind
+- [x] Blind Signature
+- [x] Unblind Signature
+- [x] Verify Signature
+- [x] Homomorphic Multiplication
+
+
+#### Usage
+- Key generation, Encryption, Decryption
+```go
+// generate key pair
+key, err := GenerateKeyPair()
+if err!=nil {
+	fmt.Println(err)
+}
+mBytes := []byte("Hi")
+m := new(big.Int).SetBytes(mBytes)
+
+// encrypt message
+c := Encrypt(m, key.PubK)
+
+// decrypt ciphertext
+d := Decrypt(c, key.PrivK)
+if m == d {
+	fmt.Println("correctly decrypted")
+}
+```
+
+- Blind signatures
+```go
+// key generation [Alice]
+key, err := GenerateKeyPair()
+if err!=nil {
+	fmt.Println(err)
+}
+
+// create new message [Alice]
+mBytes := []byte("Hi")
+m := new(big.Int).SetBytes(mBytes)
+
+// define r value [Alice]
+rVal := big.NewInt(int64(101))
+
+// blind message [Alice]
+mBlinded := Blind(m, rVal, key.PubK)
+
+// Blind Sign the blinded message [Bob]
+sigma := BlindSign(mBlinded, key.PrivK)
+
+// unblind the blinded signed message, and get the signature of the message [Alice]
+mSigned := Unblind(sigma, rVal, key.PubK)
+
+// verify the signature [Alice/Bob/Trudy]
+verified := Verify(m, mSigned, key.PubK)
+if !verified {
+	fmt.Println("signature could not be verified")
+}
+```
+
+- Homomorphic Multiplication
+```go
+// key generation [Alice]
+key, err := GenerateKeyPair()
+if err!=nil {
+	fmt.Println(err)
+}
+
+// define values [Alice]
+n1 := big.NewInt(int64(11))
+n2 := big.NewInt(int64(15))
+
+// encrypt the values [Alice]
+c1 := Encrypt(n1, key.PubK)
+c2 := Encrypt(n2, key.PubK)
+
+// compute homomorphic multiplication with the encrypted values [Bob]
+c3c4 := HomomorphicMul(c1, c2, key.PubK)
+
+// decrypt the result [Alice]
+d := Decrypt(c3c4, key.PrivK)
+
+// check that the result is the expected
+if !bytes.Equal(new(big.Int).Mul(n1, n2).Bytes(), d.Bytes()) {
+	fmt.Println("decrypted result not equal to expected result")
+}
+```