Linux下如何使用OpenSSL進行端口掃描

在 Linux 下，OpenSSL 本身并不直接提供端口掃描功能。但是，你可以使用 OpenSSL 的 s_client 命令來檢查特定端口的連接狀態。以下是如何使用 OpenSSL 進行端口掃描的方法：

1. 打開終端。

2. 輸入以下命令，將 hostname 替換為目標主機的域名或 IP 地址，將 port 替換為要掃描的端口號：

openssl s_client -connect hostname:port

例如，要檢查 example.com 上的端口 80 是否開放，可以使用以下命令：

openssl s_client -connect example.com:80

3. 按 Enter 鍵運行命令。如果端口處于監聽狀態并且連接成功，你將看到類似于以下的輸出：

CONNECTED(00000003)
depth=2 O = Digital Signature Trust Co., CN = DST Root CA X3
verify error:num=19:self signed certificate in certificate chain
verify return:1
depth=2 O = Digital Signature Trust Co., CN = DST Root CA X3
verify return:1
depth=0 CN = example.com
verify return:1
---
Certificate chain
 0 s:CN = example.com
   i:C = US, O = Let's Encrypt, CN = R3
 1 s:C = US, O = Let's Encrypt, CN = R3
   i:O = Digital Signature Trust Co., CN = DST Root CA X3
---
Server certificate
-----BEGIN CERTIFICATE-----
MIIDdzCCAl+gAwIBAgIEbTJ9zANBgkqhkiG9w0BAQsFADBzMQswCQYDVQQGEwJV
...
-----END CERTIFICATE-----
subject=CN=example.com
issuer=C = US, O = Let's Encrypt, CN = R3
---
No client certificate CA names sent
Peer signing digest: SHA256
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 3544 bytes and written 394 bytes
Verification error: self signed certificate in certificate chain
---
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 19 (self signed certificate in certificate chain)
---

如果端口未開放或連接失敗，你將看到類似于以下的輸出：

139652025286144:error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate:s3_pkt.c:1332:SSL alert number 42
139652025286144:error:1409E0E5:SSL routines:ssl3_write_bytes:ssl handshake failure:s3_pkt.c:877:
---
no peer certificate available
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 0 bytes and written 394 bytes
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
---
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : 0
    Session-ID: 
    Session-ID-ctx: 
    Master-Key: 
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1633019202
    Timeout   : 7200 (sec)
    Verify return code: 19 (self signed certificate in certificate chain)
---

請注意，這種方法只能檢查單個端口，而不能掃描多個端口。如果你需要掃描多個端口，可以考慮使用 nmap 等專門的端口掃描工具。