diff --git a/Cargo.lock b/Cargo.lock
index 10caf37..77bcae8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -678,6 +678,19 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "chacha20poly1305"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "10cd79432192d1c0f4e1a0fef9527696cc039165d729fb41b3f4f4f354c2dc35"
+dependencies = [
+ "aead 0.5.2",
+ "chacha20 0.9.1",
+ "cipher 0.4.4",
+ "poly1305 0.8.0",
+ "zeroize",
+]
+
 [[package]]
 name = "chrono"
 version = "0.4.44"
@@ -700,6 +713,7 @@ checksum = "773f3b9af64447d2ce9850330c473515014aa235e6a783b02db81ff39e4a3dad"
 dependencies = [
  "crypto-common 0.1.7",
  "inout 0.1.4",
+ "zeroize",
 ]
 
 [[package]]
@@ -2678,6 +2692,8 @@ dependencies = [
  "bcrypt",
  "byteorder",
  "bytes",
+ "chacha20 0.9.1",
+ "chacha20poly1305",
  "chrono",
  "cipher 0.4.4",
  "clap",
@@ -2694,9 +2710,11 @@ dependencies = [
  "log",
  "md5 0.8.0",
  "nix 0.29.0",
+ "poly1305 0.8.0",
  "postgres",
  "pulldown-cmark",
  "rand 0.8.6",
+ "rayon",
  "regex",
  "rusqlite",
  "russh",
diff --git a/data/auth.sqlite b/data/auth.sqlite
index 1712087..6797d40 100644
Binary files a/data/auth.sqlite and b/data/auth.sqlite differ
diff --git a/markbase-core/Cargo.toml b/markbase-core/Cargo.toml
index fdfe203..ff5c0c5 100644
--- a/markbase-core/Cargo.toml
+++ b/markbase-core/Cargo.toml
@@ -59,6 +59,9 @@ aes = "0.8"
 ctr = "0.9"
 cipher = "0.4"
 aes-gcm = "0.10"  # Phase 1: AES-256-GCM AEAD（性能优化）
+chacha20 = "0.9"   # Phase 5: ChaCha20 stream cipher（OpenSSH chacha20-poly1305）
+poly1305 = "0.8"   # Phase 5: Poly1305 authenticator（OpenSSH chacha20-poly1305）
+chacha20poly1305 = "0.10"  # Phase 5: ChaCha20-Poly1305 AEAD（备用）
 nix = { version = "0.29", features = ["poll", "fs"] }  # Phase 14: OpenSSH风格的poll()和非阻塞I/O（fs feature包含fcntl）
 rusty-s3 = "0.10"     # S3 API 签名（AWS Signature V4）
 ureq = "2.12"          # 輕量同步 HTTP 客戶端
diff --git a/markbase-core/src/ssh_server/cipher.rs b/markbase-core/src/ssh_server/cipher.rs
index e3fa05d..af5d632 100644
--- a/markbase-core/src/ssh_server/cipher.rs
+++ b/markbase-core/src/ssh_server/cipher.rs
@@ -8,6 +8,10 @@ use aes_gcm::{
     aead::{Aead, KeyInit, Payload},
     Aes256Gcm, Nonce, // Phase 1: AES-256-GCM AEAD（性能优化）
 };
+use chacha20poly1305::{
+    aead::{Aead as ChaAead, KeyInit as ChaKeyInit, Payload as ChaPayload},
+    ChaCha20Poly1305, Key as ChaKey, Nonce as ChaNonce, // Phase 5: ChaCha20-Poly1305 AEAD
+};
 use anyhow::{anyhow, Result};
 use byteorder::{BigEndian, WriteBytesExt};
 use cipher::{KeyIvInit, StreamCipher};
@@ -41,8 +45,9 @@ pub struct EncryptionContext {
 /// Phase 1: 加密模式选择（AES-CTR vs AES-GCM）
 #[derive(Debug, Clone, PartialEq)]
 pub enum CipherMode {
-    AesCtr,   // AES-128-CTR + HMAC-SHA256（MtE模式，兼容性）
-    AesGcm,   // AES-256-GCM（AEAD模式，性能优化）
+    AesCtr,      // AES-128-CTR + HMAC-SHA256（MtE模式，兼容性）
+    AesGcm,      // AES-256-GCM（AEAD模式，性能优化）
+    ChaChaPoly,  // ChaCha20-Poly1305（AEAD模式，OpenSSH默认）
 }
 
 impl Default for EncryptionContext {
@@ -389,6 +394,87 @@ impl EncryptedPacket {
                 padding: random_padding,
                 mac: ciphertext[ciphertext.len()-16..].to_vec(), // AES-GCM tag (last 16 bytes)
             })
+        } else if encryption_ctx.cipher_mode == CipherMode::ChaChaPoly {
+            // ChaCha20-Poly1305 AEAD 模式（Phase 5: OpenSSH默认）
+            info!("Creating ChaCha20-Poly1305 encrypted packet: payload_len={}", payload_length);
+            
+            // ChaCha20-Poly1305: packet_length 不加密（作为 AAD）
+            // 构建plaintext payload（padding_length + payload + padding）
+            let total_plaintext_size = 1 + payload_length + padding_length as usize;
+            let mut plaintext_payload_buffer = SshBuf::with_capacity(total_plaintext_size);
+            plaintext_payload_buffer.put(&[padding_length])?;
+            plaintext_payload_buffer.put(plaintext_payload)?;
+            
+            let mut random_padding = vec![0u8; padding_length as usize];
+            use rand::RngCore;
+            rand::thread_rng().fill_bytes(&mut random_padding);
+            plaintext_payload_buffer.put(&random_padding)?;
+            
+            // ChaCha20-Poly1305 key: 32 bytes
+            let key_bytes = if is_server_to_client {
+                &encryption_ctx.encryption_key_stoc
+            } else {
+                &encryption_ctx.encryption_key_ctos
+            };
+            
+            // ChaCha20-Poly1305 nonce: 12 bytes = sequence_number (4 bytes) + iv (8 bytes)
+            let sequence_number = if is_server_to_client {
+                encryption_ctx.sequence_number_stoc
+            } else {
+                encryption_ctx.sequence_number_ctos
+            };
+            let iv_bytes = if is_server_to_client {
+                &encryption_ctx.iv_stoc
+            } else {
+                &encryption_ctx.iv_ctos
+            };
+            
+            // Nonce: sequence_number (4 bytes big-endian) + iv (8 bytes)
+            let nonce_bytes: [u8; 12] = {
+                let mut n = [0u8; 12];
+                n[0..4].copy_from_slice(&sequence_number.to_be_bytes());
+                n[4..12].copy_from_slice(&iv_bytes[..8]);
+                n
+            };
+            
+            info!("ChaCha20-Poly1305 encrypt: nonce={:?}, key_len={}", nonce_bytes, key_bytes.len());
+            
+            // ChaCha20-Poly1305 加密（AEAD: payload + Poly1305 tag）
+            let cipher = ChaCha20Poly1305::new(ChaKey::from_slice(&key_bytes[..32]));
+            let nonce = ChaNonce::from_slice(&nonce_bytes);
+            
+            // AAD: packet_length (4 bytes, plaintext)
+            let packet_length_bytes = (packet_length as u32).to_be_bytes();
+            
+            // ChaCha20-Poly1305 encrypt: ciphertext = encrypt(payload, nonce, AAD=packet_length)
+            let ciphertext = cipher.encrypt(nonce, ChaPayload {
+                msg: plaintext_payload_buffer.ptr(),
+                aad: &packet_length_bytes,
+            }).map_err(|e| anyhow!("ChaCha20-Poly1305 encryption failed: {}", e))?;
+            
+            info!("ChaCha20-Poly1305 ciphertext size: {} bytes (payload + 16-byte tag)", ciphertext.len());
+            
+            // ChaCha20-Poly1305 packet structure (similar to AES-GCM):
+            // [packet_length (4 bytes plaintext)] [ciphertext (payload + padding + 16-byte tag)]
+            let mut full_packet = SshBuf::with_capacity(4 + ciphertext.len());
+            full_packet.put(&(packet_length as u32).to_be_bytes())?;
+            full_packet.put(&ciphertext)?;
+            let full_packet_vec = full_packet.into_vec();
+            
+            // 更新sequence number
+            if is_server_to_client {
+                encryption_ctx.sequence_number_stoc += 1;
+            } else {
+                encryption_ctx.sequence_number_ctos += 1;
+            }
+            
+            Ok(Self {
+                packet_length: packet_length as u32,
+                padding_length,
+                payload: full_packet_vec, // ChaCha20-Poly1305: packet_length (plaintext) + ciphertext
+                padding: random_padding,
+                mac: ciphertext[ciphertext.len()-16..].to_vec(), // Poly1305 tag (last 16 bytes)
+            })
         } else {
             // AES-CTR MtE 模式（原有逻辑）
             info!(
@@ -615,6 +701,104 @@ impl EncryptedPacket {
                 padding,
                 mac, // AES-GCM tag
             })
+        } else if encryption_ctx.cipher_mode == CipherMode::ChaChaPoly {
+            // ChaCha20-Poly1305 AEAD 模式（Phase 5: OpenSSH默认）
+            info!("Reading ChaCha20-Poly1305 AEAD packet (packet_length plaintext)");
+            
+            // 1. 读取 plaintext packet_length (4 bytes)
+            let mut packet_length_bytes = [0u8; 4];
+            stream.read_exact(&mut packet_length_bytes)?;
+            let packet_length = u32::from_be_bytes(packet_length_bytes);
+            
+            info!("Read plaintext packet_length: {}", packet_length);
+            
+            // 2. 合理性检查
+            if packet_length > 35000 {
+                return Err(anyhow!("Invalid packet_length: {}", packet_length));
+            }
+            
+            // 3. 计算 ciphertext 长度
+            // ciphertext = padding_length(1) + payload + padding + Poly1305_tag(16)
+            let ciphertext_length = packet_length as usize + 16; // packet content + 16-byte tag
+            
+            info!("Ciphertext length: {} bytes (payload + 16-byte tag)", ciphertext_length);
+            
+            // 4. 读取 ciphertext
+            let mut ciphertext = vec![0u8; ciphertext_length];
+            stream.read_exact(&mut ciphertext)?;
+            
+            info!("Read ciphertext: {} bytes", ciphertext.len());
+            
+            // 5. ChaCha20-Poly1305 nonce: 12 bytes = sequence_number (4 bytes) + iv (8 bytes)
+            let sequence_number = if is_client_to_server {
+                encryption_ctx.sequence_number_ctos
+            } else {
+                encryption_ctx.sequence_number_stoc
+            };
+            
+            let iv_bytes = if is_client_to_server {
+                &encryption_ctx.iv_ctos
+            } else {
+                &encryption_ctx.iv_stoc
+            };
+            
+            // Nonce: sequence_number (4 bytes big-endian) + iv (8 bytes)
+            let nonce_bytes: [u8; 12] = {
+                let mut n = [0u8; 12];
+                n[0..4].copy_from_slice(&sequence_number.to_be_bytes());
+                n[4..12].copy_from_slice(&iv_bytes[..8]);
+                n
+            };
+            
+            info!("ChaCha20-Poly1305 nonce: seq={}, iv[:8]={:?}, nonce={:?}", sequence_number, &iv_bytes[..8], nonce_bytes);
+            
+            // 6. ChaCha20-Poly1305 key: 32 bytes
+            let key_bytes = if is_client_to_server {
+                &encryption_ctx.encryption_key_ctos
+            } else {
+                &encryption_ctx.encryption_key_stoc
+            };
+            
+            // 7. ChaCha20-Poly1305 解密（AEAD: decrypt(ciphertext, nonce, AAD=packet_length)）
+            let cipher = ChaCha20Poly1305::new(ChaKey::from_slice(&key_bytes[..32]));
+            let nonce = ChaNonce::from_slice(&nonce_bytes);
+            
+            // AAD: packet_length (4 bytes plaintext)
+            let plaintext_payload_buffer = cipher.decrypt(nonce, ChaPayload {
+                msg: ciphertext.as_slice(),
+                aad: &packet_length_bytes,
+            }).map_err(|e| anyhow!("ChaCha20-Poly1305 decryption failed: {}", e))?;
+            
+            info!("ChaCha20-Poly1305 decrypted payload: {} bytes", plaintext_payload_buffer.len());
+            
+            // 8. 提取 padding_length, payload, padding
+            let padding_length = plaintext_payload_buffer[0];
+            let payload_length = packet_length as usize - padding_length as usize - 1;
+            
+            info!("ChaCha20-Poly1305: padding_length={}, payload_length={}", padding_length, payload_length);
+            
+            let payload = plaintext_payload_buffer[1..1 + payload_length].to_vec();
+            let padding = Vec::new();  // ChaCha20-Poly1305: padding 不需要存储
+            
+            // 9. 提取 Poly1305 tag (last 16 bytes of ciphertext)
+            let mac = ciphertext[ciphertext.len()-16..].to_vec();
+            
+            info!("ChaCha20-Poly1305 tag (16 bytes): {:?}", &mac);
+            
+            // 10. 更新sequence number
+            if is_client_to_server {
+                encryption_ctx.sequence_number_ctos += 1;
+            } else {
+                encryption_ctx.sequence_number_stoc += 1;
+            }
+            
+            Ok(Self {
+                packet_length,
+                padding_length,
+                payload, // Just the SSH payload (not full packet)
+                padding,
+                mac, // Poly1305 tag
+            })
         } else {
             // AES-CTR MtE 模式（原有逻辑）
             info!("Reading AES-CTR encrypted packet (packet_length encrypted)");
diff --git a/markbase-core/src/ssh_server/server.rs b/markbase-core/src/ssh_server/server.rs
index 8cdb0b4..2a169a9 100644
--- a/markbase-core/src/ssh_server/server.rs
+++ b/markbase-core/src/ssh_server/server.rs
@@ -306,12 +306,15 @@ fn perform_complete_kex_exchange(
     let session_keys = kex_state.exchange_handler.compute_session_keys()?;
     let mut encryption_ctx = EncryptionContext::from_session_keys(&session_keys);
     
-    // Phase 1: 根据 KEX 协商结果设置加密模式（AES-GCM vs AES-CTR）
+    // Phase 1+5: 根据 KEX 协商结果设置加密模式（ChaCha20-Poly1305 / AES-GCM / AES-CTR）
     let encryption_algorithm = &kex_result.encryption_stoc;
     info!("KEX negotiated encryption algorithm: {}", encryption_algorithm);
     
     use crate::ssh_server::cipher::CipherMode;
-    if encryption_algorithm.contains("gcm") {
+    if encryption_algorithm.contains("chacha20") {
+        info!("Setting cipher mode to ChaCha20-Poly1305 (AEAD)");
+        encryption_ctx.set_cipher_mode(CipherMode::ChaChaPoly)?;
+    } else if encryption_algorithm.contains("gcm") {
         info!("Setting cipher mode to AES-GCM (AEAD)");
         encryption_ctx.set_cipher_mode(CipherMode::AesGcm)?;
     } else {