curl -vvvでHTTPS(TLS通信)を簡易的に覗く

5 min read

httpsunixtls

こんにちは、無能です。

はじめに

HTTPS自体はTLS通信であり、HTTP over TLSの通りでHTTP通信をTLS通信でラップされたものでTLS通信だけに焦点を当てるとHTTPS通信に対応したドメインに対してのリクエストとは違ったものになってしまうのでcurl -vvvで詳細デバッグすることでclient helloからその通信を確認することができます。とはいったものの偶然見つけたものです。

見てみる

さて、以下のようにして覗いてみます。

curl -vvv -sl
-vvv # 詳細デバッグオプション
-s # サイレントモード、なくてもよい
-I # ヘッダーだけ標準出力

それでは見てみましょう。

$ curl -vvv https://soulminingrig.com/ -sI
19:30:07.019276 [0-x] == Info: [READ] client_reset, clear readers
19:30:07.064770 [0-0] == Info: Host soulminingrig.com:443 was resolved.
19:30:07.065031 [0-0] == Info: IPv6: (none)
19:30:07.065180 [0-0] == Info: IPv4: 167.179.75.206
19:30:07.065413 [0-0] == Info: [HTTPS-CONNECT] adding wanted h2
19:30:07.065587 [0-0] == Info: [HTTPS-CONNECT] added
19:30:07.065718 [0-0] == Info: [HTTPS-CONNECT] connect, init
19:30:07.065881 [0-0] == Info:   Trying 167.179.75.206:443...
19:30:07.066065 [0-0] == Info: [HTTPS-CONNECT] connect -> 0, done=0
19:30:07.066197 [0-0] == Info: [HTTPS-CONNECT] Curl_conn_connect(block=0) -> 0, done=0
19:30:07.066400 [0-0] == Info: [HTTPS-CONNECT] adjust_pollset -> 1 socks
19:30:07.083945 [0-0] == Info: [HTTPS-CONNECT] connect -> 0, done=0
19:30:07.084308 [0-0] == Info: [HTTPS-CONNECT] Curl_conn_connect(block=0) -> 0, done=0
19:30:07.084750 [0-0] == Info: [HTTPS-CONNECT] adjust_pollset -> 1 socks
19:30:07.095330 [0-0] == Info: [SSL] cf_connect()
19:30:07.095574 [0-0] == Info: [SSL] ossl_connect, step1
19:30:07.098502 [0-0] == Info: ALPN: curl offers h2,http/1.1
19:30:07.098614 [0-0] == Info: [SSL] ossl_connect, step2
19:30:07.099069 [0-0] => Send SSL data, 5 bytes (0x5)
0000: .....
19:30:07.099205 [0-0] == Info: TLSv1.3 (OUT), TLS handshake, Client hello (1):
19:30:07.099360 [0-0] => Send SSL data, 1563 bytes (0x61b)
~省略~

と、すごい量の文字列が出てきました・・・。

通信確認

ここで443番ポートでのDNSの名前解決ができました

19:30:07.064770 [0-0] == Info: Host soulminingrig.com:443 was resolved.

ここでh2、HTTP/2での接続を求めて接続できました

19:30:07.065413 [0-0] == Info: [HTTPS-CONNECT] adding wanted h2
19:30:07.065587 [0-0] == Info: [HTTPS-CONNECT] added
19:30:07.065718 [0-0] == Info: [HTTPS-CONNECT] connect, init
19:30:07.065881 [0-0] == Info:   Trying 167.179.75.206:443...
19:30:07.066065 [0-0] == Info: [HTTPS-CONNECT] connect -> 0, done=0

そしてついにSSL/TLS通信が始まりました

19:30:07.095330 [0-0] == Info: [SSL] cf_connect()
19:30:07.095574 [0-0] == Info: [SSL] ossl_connect, step1
19:30:07.098502 [0-0] == Info: ALPN: curl offers h2,http/1.1
19:30:07.098614 [0-0] == Info: [SSL] ossl_connect, step2
19:30:07.099069 [0-0] => Send SSL data, 5 bytes (0x5)

そして、TLS1.3でついにプロトコル上のclient helloのTLS handshakeがはじまりました！

19:30:07.099205 [0-0] == Info: TLSv1.3 (OUT), TLS handshake, Client hello (1):

クライアントの送信としてパケット送信が始まります

19:30:07.099205 [0-0] == Info: TLSv1.3 (OUT), TLS handshake, Client hello (1):
19:30:07.099360 [0-0] => Send SSL data, 1563 bytes (0x61b)
0000: .........r.q.....GC...._4....k..C.P... ..?...x...HT..09..z4b....
0040: ..,9....<.......,.0.........+./...$.(.k.#.'.g.....9.....3.....=.
0080: <.5./..................soulminingrig.com........................
00c0: .............h2.http/1.1.........1.....6.4......................
0100: ...............................+........-.....3...........RIw..7

この時点で、リクエスト自体にはドメインであるsoulminingrig.comが平文で送られてサーバー側がSNIに対応していれば整合が取れます

19:30:07.105068 [0-0] == Info: [SSL] ossl_bio_cf_out_write(len=1568) -> 0, 1568
19:30:07.105244 [0-0] == Info: [SSL] ossl_bio_cf_in_read(len=5) -> 81, 0
19:30:07.105355 [0-0] == Info: [SSL] ossl_populate_x509_store, path=/etc/ssl/certs/ca-certificates.crt, blob=0
19:30:07.114557 [0-0] == Info:  CAfile: /etc/ssl/certs/ca-certificates.crt
19:30:07.114669 [0-0] == Info:  CApath: none
19:30:07.114768 [0-0] == Info: [SSL] SSL_connect() -> err=-1, detail=2
19:30:07.114903 [0-0] == Info: [SSL] SSL_connect() -> want recv
19:30:07.115050 [0-0] == Info: [SSL] cf_connect() -> 0, done=0

この時点で、クライアント側の保有するRoot証明書を用意しています
まだ接続は確立していないですね
Let's Encryptの場合はISRG Root X1にあたるもののようです
Chain of Trust - Let's Encrypt

$ grep -A 3 "ISRG Root X1" /etc/ssl/certs/ca-certificates.crt
# ISRG Root X1
-----BEGIN CERTIFICATE-----
MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh

そしてServer Helloが帰ってきました！

19:30:07.178149 [0-0] == Info: [SSL] ossl_bio_cf_in_read(len=122) -> 0, 122
19:30:07.178363 [0-0] == Info: TLSv1.3 (IN), TLS handshake, Server hello (2):
19:30:07.178583 [0-0] <= Recv SSL data, 122 bytes (0x7a)
0000: ...v....y'...>........&.....,5O....... ..?...x...HT..09..z4b....
0040: ..,9.........+.....3.$... F........`~..l[..uhE..F.P?..V..6
19:30:07.179600 [0-0] == Info: [SSL] ossl_bio_cf_in_read(len=5) -> 0, 5
19:30:07.179730 [0-0] <= Recv SSL data, 5 bytes (0x5)

そして、サーバー側から証明書が帰ってきました

19:30:07.183139 [0-0] <= Recv SSL data, 2049 bytes (0x801)
0000: ...........0...0.................g...4...C..0...*.H.=...021.0...
0040: U....US1.0...U....Let's Encrypt1.0...U....E50...250714140356Z..2
0080: 51012140355Z0.1.0...U....soulminingrig.com0Y0...*.H.=....*.H.=..
00c0: ..B...V...$.....}.hN.f......n@F&...GR.....-.....?z]6d.=..<..eu..

サーバー側が持つ秘密鍵を使って署名が送られてきました

0000: .
19:30:07.199683 [0-0] == Info: TLSv1.3 (IN), TLS handshake, CERT verify (15):
19:30:07.199941 [0-0] <= Recv SSL data, 79 bytes (0x4f)

ここでTLS handshakeがついに終了し確立されました

19:30:07.202057 [0-0] == Info: TLSv1.3 (IN), TLS handshake, Finished (20):

あまり見れないTLS handshake

最初、ChatGPTとかに聞いてもWiresharkとかを使えと言われながらなかなかWiresharkだとノイズになるものも多いので簡易的に確認できるものがないかなあと思っていましたがそういえば、と思い試したらうまくいきました。
TLS handshakeが失敗するパターンとして、以下で確認してみても面白いかもしれません。
badssl.com

$ curl -vvv -sl https://wrong.host.badssl.com/
19:50:53.161049 [0-x] == Info: [READ] client_reset, clear readers
19:50:53.202041 [0-0] == Info: Host wrong.host.badssl.com:443 was resolved.
19:50:53.202233 [0-0] == Info: IPv6: (none)
19:50:53.202326 [0-0] == Info: IPv4: 104.154.89.105
19:50:53.202496 [0-0] == Info: [HTTPS-CONNECT] adding wanted h2
~~~
19:50:53.759424 [0-0] == Info: SSL connection using TLSv1.2 / ECDHE-RSA-AES128-GCM-SHA256 / secp256r1 / rsaEncryption
19:50:53.759894 [0-0] == Info: ALPN: server accepted http/1.1
19:50:53.760124 [0-0] == Info: [SSL] ossl_connect, step3
19:50:53.760337 [0-0] == Info: Server certificate:
19:50:53.760541 [0-0] == Info:  subject: CN=*.badssl.com
19:50:53.760763 [0-0] == Info:  start date: Jul 15 20:02:58 2025 GMT
19:50:53.761029 [0-0] == Info:  expire date: Oct 13 20:02:57 2025 GMT
19:50:53.761406 [0-0] == Info:  subjectAltName does not match hostname wrong.host.badssl.com
19:50:53.761853 [0-0] == Info: SSL: no alternative certificate subject name matches target hostname 'wrong.host.badssl.com'
19:50:53.762409 [0-0] == Info: [SSL] cf_connect() -> 60, done=0

この場合、*.badssl.comで証明書取ってしまっていて*.host.badssl.comでワイルドカード証明書取得していないといけないので間違えていることで怒られていますね。

それではまた。よろしくおねがいします。

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