SSL/TLS handshake timeout with server preferring DHE cipher (with 4096 bit DH key)

[chaosbiber]

Using WiFiClientSecure or HTTPClient I couldn't connect to some servers, especially running my customised nginx configuration.
Using wireshark and later enabling verbose output I found that the handshake wouldn't finish.

16:45:09.102 -> Starting connection to server...
16:45:09.102 -> [V][ssl_client.cpp:53] start_ssl_client(): Free internal heap before TLS 278304
16:45:09.102 -> [V][ssl_client.cpp:55] start_ssl_client(): Starting socket
[V][ssl_client.cpp:90] start_ssl_client(): Seeding the random number generator
16:45:09.139 -> [V][ssl_client.cpp:99] start_ssl_client(): Setting up the SSL/TLS structure...
16:45:09.139 -> [V][ssl_client.cpp:112] start_ssl_client(): Loading CA cert
16:45:09.172 -> [V][ssl_client.cpp:177] start_ssl_client(): Setting hostname for TLS session...
16:45:09.172 -> [V][ssl_client.cpp:192] start_ssl_client(): Performing the SSL/TLS handshake...
[E][ssl_client.cpp:33] handle_error(): SSL - The connection indicated an EOF
16:45:44.955 -> [E][ssl_client.cpp:35] handle_error(): MbedTLS message code: -29312
16:45:44.955 -> [E][WiFiClientSecure.cpp:132] connect(): start_ssl_client: -29312
16:45:44.991 -> [V][ssl_client.cpp:245] stop_ssl_socket(): Cleaning SSL connection.
16:45:44.991 -> Connection failed!

After changing the server's cipher suite to prefer ECDH it works:

16:43:56.575 -> Starting connection to server...
16:43:56.575 -> [V][ssl_client.cpp:53] start_ssl_client(): Free internal heap before TLS 278448
16:43:56.575 -> [V][ssl_client.cpp:55] start_ssl_client(): Starting socket
[V][ssl_client.cpp:90] start_ssl_client(): Seeding the random number generator
16:43:56.747 -> [V][ssl_client.cpp:99] start_ssl_client(): Setting up the SSL/TLS structure...
16:43:56.747 -> [V][ssl_client.cpp:112] start_ssl_client(): Loading CA cert
16:43:56.747 -> [V][ssl_client.cpp:177] start_ssl_client(): Setting hostname for TLS session...
16:43:56.782 -> [V][ssl_client.cpp:192] start_ssl_client(): Performing the SSL/TLS handshake...
[V][ssl_client.cpp:213] start_ssl_client(): Verifying peer X.509 certificate...
16:43:57.991 -> [V][ssl_client.cpp:222] start_ssl_client(): Certificate verified.
16:43:57.991 -> [V][ssl_client.cpp:237] start_ssl_client(): Free internal heap after TLS 236888
16:43:57.991 -> [V][ssl_client.cpp:276] send_ssl_data(): Writing HTTP request...

Comparing the listed ciphers from ssllab's server test and howsmyssl's client test the first common cipher with the problematic server config was
TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0x9f) DH 4096 bits FS
I guess the problem is the big custom dh-key?

It's not a big problem as my newer config already preferred the curves, but still wanted to report it. Can we check if the DH is too big before choosing that cipher?

Hardware:

Board: NodeMCU ESP-32s
Core Installation version: 1.0.2
IDE name: Arduino IDE

Sketch:

https://github.com/espressif/arduino-esp32/blob/master/libraries/WiFiClientSecure/examples/WiFiClientSecure/WiFiClientSecure.ino
replacing server with a problematic one

[chegewara]

If i am correct esp-idf works with 2048 bits certificates, i think me and some other people got issues with 1024 or 4096 bits keys. But it was some time ago so i may be wrong.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[stale]

This stale issue has been automatically closed. Thank you for your contributions.

[bjdshp]

Getting same failure using this....

https://github.com/mobizt/Firebase-ESP-Client

Tried putting a 100 mF capacitor between ground and 3.3, but couldn't get it to write firmware. Any suggestions?

[Alexvillenbermejo]

sane error