diff --git a/src/main.rs b/src/main.rs
index da943fc..98c777c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,6 +4,7 @@ use std::fmt::Display;
 use hex::{FromHex, ToHex};
 use inquire::{validator::Validation, CustomType, Select, Text};
 
+mod pha;
 mod rsa;
 mod utils;
 
@@ -61,7 +62,7 @@ fn generate_key() -> anyhow::Result<()> {
         })
         .prompt()?;
 
-    let (public_key, private_key) = rsa::keygen(bits);
+    let (public_key, private_key) = pha::keygen(bits);
 
     println!();
     println!("Generated key with {} bits", private_key.bits());
@@ -76,11 +77,10 @@ fn generate_key() -> anyhow::Result<()> {
 }
 
 fn calculate_key() -> anyhow::Result<()> {
-    let p = CustomType::new("Enter prime p").prompt()?;
-    let q = CustomType::new("Enter prime q").prompt()?;
-    let e = CustomType::new("Enter public exponent e").prompt()?;
+    let n = CustomType::new("Enter prime n").prompt()?;
+    let e = CustomType::new("Enter e").prompt()?;
 
-    let (public_key, private_key) = rsa::calculate_key(p, q, e);
+    let (public_key, private_key) = pha::calculate_key(n, e);
 
     println!();
     println!("Public key:");
@@ -98,11 +98,19 @@ fn encrypt() -> anyhow::Result<()> {
 
     let data = Text::new("Enter data").prompt()?;
 
-    let public_key = rsa::PublicKey::new(n, e);
+    let public_key = pha::PublicKey::new(n, e);
     let chunk_size = (public_key.bits() / 8) as usize;
     let safe_chunk_size = chunk_size - 1;
     let data = data.as_bytes();
 
+    if chunk_size < 2 {
+        println!(
+            "This key cannot encrypt byte data! Key size {} bits is less than 16 bits.",
+            public_key.bits()
+        );
+        return Ok(());
+    }
+
     println!();
     println!("data (raw) = {:?}", data);
 
@@ -130,7 +138,7 @@ fn decrypt() -> anyhow::Result<()> {
 
     let encrypted = Text::new("Enter encrypted data").prompt()?;
 
-    let private_key = rsa::PrivateKey::new(n, d);
+    let private_key = pha::PrivateKey::new(n, d);
     let chunk_size = (private_key.bits() / 8) as usize;
     let encrypted = Vec::<u8>::from_hex(encrypted)?;
 
diff --git a/src/pha.rs b/src/pha.rs
new file mode 100644
index 0000000..836c5b0
--- /dev/null
+++ b/src/pha.rs
@@ -0,0 +1,92 @@
+#![allow(unused)]
+
+use std::fmt::{Display, Formatter};
+
+use num::BigUint;
+
+use crate::utils;
+
+pub struct PublicKey {
+    n: BigUint,
+    e: BigUint,
+}
+
+impl PublicKey {
+    pub fn new(n: BigUint, e: BigUint) -> Self {
+        Self { n, e }
+    }
+
+    pub fn encrypt(&self, chunk: &[u8]) -> Vec<u8> {
+        let message = BigUint::from_bytes_le(chunk);
+
+        let encrypted = message.modpow(&self.e, &self.n);
+        encrypted.to_bytes_le()
+    }
+
+    pub fn bits(&self) -> u64 {
+        self.n.bits()
+    }
+}
+
+impl Display for PublicKey {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "(n = {:?}, e = {:?})", self.n, self.e)
+    }
+}
+
+pub struct PrivateKey {
+    n: BigUint,
+    d: BigUint,
+}
+
+impl PrivateKey {
+    pub fn new(n: BigUint, d: BigUint) -> Self {
+        Self { n, d }
+    }
+
+    pub fn decrypt(&self, chunk: &[u8]) -> Vec<u8> {
+        let encrypted = BigUint::from_bytes_le(chunk);
+
+        let decrypted = encrypted.modpow(&self.d, &self.n);
+        decrypted.to_bytes_le()
+    }
+
+    pub fn bits(&self) -> u64 {
+        self.n.bits()
+    }
+}
+
+impl Display for PrivateKey {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "(n = {:?}, d = {:?})", self.n, self.d)
+    }
+}
+
+pub fn gen_n_e(bits: u64) -> (BigUint, BigUint) {
+    let mut numbers = utils::generate_n_primes(2, bits);
+    let a1 = numbers.pop().unwrap();
+    let a2 = numbers.pop().unwrap();
+
+    let (n, e) = if a1 < a2 { (a2, a1) } else { (a1, a2) };
+
+    (n, e)
+}
+
+pub fn keygen(bits: u64) -> (PublicKey, PrivateKey) {
+    let (mut n, mut e) = gen_n_e(bits);
+    while n.bits() < bits {
+        (n, e) = gen_n_e(bits);
+    }
+
+    calculate_key(n, e)
+}
+
+pub fn calculate_key(n: BigUint, e: BigUint) -> (PublicKey, PrivateKey) {
+    let one = BigUint::from(1u8);
+    let d = e.modinv(&(&n - one)).unwrap();
+
+    let public_key = PublicKey::new(n.clone(), e);
+    let private_key = PrivateKey::new(n, d);
+
+    (public_key, private_key)
+}
diff --git a/src/rsa.rs b/src/rsa.rs
index 2dc7d11..5869eb7 100644
--- a/src/rsa.rs
+++ b/src/rsa.rs
@@ -76,7 +76,7 @@ fn gen_n_phi(bits: u64) -> (BigUint, BigUint) {
 pub fn keygen(bits: u64) -> (PublicKey, PrivateKey) {
     let (mut n, mut phi) = gen_n_phi(bits);
     while n.bits() < bits {
-       (n, phi) = gen_n_phi(bits);
+        (n, phi) = gen_n_phi(bits);
     }
 
     let n = n;