Python 3.10 does not appear to respecting the OpenSSL configuration within linux. Testing completed using Pyenv on both Ubuntu 20.04.4 and Centos-8. Note PEP 644 which requires OpenSSL >= 1.1.1 is released in Python 3.10.

We operate behind a corporate proxy / firewall which causes an SSL error where the Diffie-Hellman key size is too small. In previous Python versions this is resolved by updating the OpenSSL configuration, e.g. downgrading the linux crypto policies `sudo update-crypto-policies --set LEGACY`. 

The issue is reproducible in both Ubuntu 20.04.4 and Centos-8. In both linux distributions the SSL error is resolvable in earlier Python version, using the OpenSSL configurations, but the configuration is not respected with Python 3.10.2.

See the details below on the kernel versions, linux distributions, and Openssl versions, many thanks in advance.

1. Python 3.10.2 Error:
(py_3_10_2) ➜  py_3_10_2 pip install --upgrade pip
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'SSLError(SSLError(1, '[SSL: DH_KEY_TOO_SMALL] dh key too small (_ssl.c:997)'))': /simple/pip/

2. Ubuntu details
uname -a
Linux Horatio 5.13.0-30-generic #33~20.04.1-Ubuntu SMP Mon Feb 7 14:25:10 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

lsb_release  -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 20.04.4 LTS
Release:	20.04
Codename:	focal

openssl version -a
OpenSSL 1.1.1f  31 Mar 2020
built on: Wed Nov 24 13:20:48 2021 UTC
platform: debian-amd64
options:  bn(64,64) rc4(16x,int) des(int) blowfish(ptr) 
compiler: gcc -fPIC -pthread -m64 -Wa,--noexecstack -Wall -Wa,--noexecstack -g -O2 -fdebug-prefix-map=/build/openssl-dnfdFp/openssl-1.1.1f=. -fstack-protector-strong -Wformat -Werror=format-security -DOPENSSL_TLS_SECURITY_LEVEL=2 -DOPENSSL_USE_NODELETE -DL_ENDIAN -DOPENSSL_PIC -DOPENSSL_CPUID_OBJ -DOPENSSL_IA32_SSE2 -DOPENSSL_BN_ASM_MONT -DOPENSSL_BN_ASM_MONT5 -DOPENSSL_BN_ASM_GF2m -DSHA1_ASM -DSHA256_ASM -DSHA512_ASM -DKECCAK1600_ASM -DRC4_ASM -DMD5_ASM -DAESNI_ASM -DVPAES_ASM -DGHASH_ASM -DECP_NISTZ256_ASM -DX25519_ASM -DPOLY1305_ASM -DNDEBUG -Wdate-time -D_FORTIFY_SOURCE=2
OPENSSLDIR: "/usr/lib/ssl"
ENGINESDIR: "/usr/lib/x86_64-linux-gnu/engines-1.1"
Seeding source: os-specific

2. Centos-8 details
uname -a
Linux localhost.localdomain 5.4.181-1.el8.elrepo.x86_64 #1 SMP Tue Feb 22 10:00:15 EST 2022 x86_64 x86_64 x86_64 GNU/Linux

cat /etc/centos-release
CentOS Stream release 8

openssl version -a
OpenSSL 1.1.1k  FIPS 25 Mar 2021
built on: Thu Dec  2 16:40:48 2021 UTC
platform: linux-x86_64
options:  bn(64,64) md2(char) rc4(16x,int) des(int) idea(int) blowfish(ptr) 
compiler: gcc -fPIC -pthread -m64 -Wa,--noexecstack -Wall -O3 -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -Wa,--noexecstack -Wa,--generate-missing-build-notes=yes -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -DOPENSSL_USE_NODELETE -DL_ENDIAN -DOPENSSL_PIC -DOPENSSL_CPUID_OBJ -DOPENSSL_IA32_SSE2 -DOPENSSL_BN_ASM_MONT -DOPENSSL_BN_ASM_MONT5 -DOPENSSL_BN_ASM_GF2m -DSHA1_ASM -DSHA256_ASM -DSHA512_ASM -DKECCAK1600_ASM -DRC4_ASM -DMD5_ASM -DAESNI_ASM -DVPAES_ASM -DGHASH_ASM -DECP_NISTZ256_ASM -DX25519_ASM -DPOLY1305_ASM -DZLIB -DNDEBUG -DPURIFY -DDEVRANDOM="\"/dev/urandom\"" -DSYSTEM_CIPHERS_FILE="/etc/crypto-policies/back-ends/openssl.config"
OPENSSLDIR: "/etc/pki/tls"
ENGINESDIR: "/usr/lib64/engines-1.1"
Seeding source: os-specific
engines:  rdrand dynamic

How did you build Python 3.10? Neither CentOS 8 nor Ubuntu 20.04 come with Python 3.10. Does your build of Python use system's OpenSSL build?

Thanks for the quick reply. On both Ubuntu and Centos, I’m installing Python using Pyenv, testing with 3.9.10 and 3.10.2. Pyenv provides a verbose install flag, I can rebuild the Python versions and review the build commands, if helpful? I’m testing with clean Linux distributions and I believe there is only one OpenSSL installed and available. I don’t know if it’s possible to gain more details from the Python ssl module to confirm? I did confirm the OpenSSL versions aligns using ssl.OPENSSL_VERSION.

Command: pyenv install 3.10.2 --verbose

https://github.com/pyenv/pyenv

I found the Python build recipes and Pyenv does appear to install OpenSSL from source. The only difference I can see, aside from the Python version, is an update on the OpenSSL versions; openssl-1.1.1l (3.9.10) to openssl-1.1.1k (3.10.2). The OpenSSL release notes do not appear to suggest anything relevant.

https://github.com/pyenv/pyenv/blob/master/plugins/python-build/share/python-build/3.10.2

https://github.com/pyenv/pyenv/blob/master/plugins/python-build/share/python-build/3.9.10

https://github.com/pyenv/pyenv/blob/master/plugins/python-build/bin/python-build

https://www.openssl.org/news/openssl-1.1.1-notes.html

This is a pyenv issue, not a Python issue. Custom builds of OpenSSL typically do not and cannot use global settings like crypto policies. They are missing distro downstream patches and use different config files.

Yes agreed, it may well be a Pyenv issue. Interestingly we can demonstrate that the global OpenSSL crypto policies is respected with the 3.9.10 version, through adjusting the policy. The ssl error occurs with the default policy setting and is resolved with the legacy policy setting. With 3.10.2 this is no longer the case. I can’t see any obvious changes to the build recipe that would cause this.

Update, the Pyenv team confirmed that they do not install OpenSSL in linux, its only installed for MacOS, and it should be built using the system OpenSSL within Linux.

We're investigating further to attempt to debug the issue. Interestingly the OpenSSL build flags for both Python versions appear to be the same.

`Trying link with OPENSSL_LDFLAGS=; OPENSSL_LIBS=-lssl -lcrypto; OPENSSL_INCLUDES=`

I've attached the build logs for both the Python 3.9.10 and 3.10.2 build, in case you're able to review. Many thanks.

https://github.com/pyenv/pyenv/issues/2257

Could you please provide the outputs of the following commands:

python3 -c "import _ssl; print(_ssl.__file__)"

ldd $(python3.10 -c "import _ssl; print(_ssl.__file__)")

strace -e openat python3.10 -c "from urllib.request import urlopen; urlopen('https://www.python.org')"


The outputs look like this on my computer:

$ python3 -c "import _ssl; print(_ssl.__file__)"
/usr/lib64/python3.10/lib-dynload/_ssl.cpython-310-x86_64-linux-gnu.so
$ ldd $(python3.10 -c "import _ssl; print(_ssl.__file__)")
        linux-vdso.so.1 (0x00007ffd1a10e000)
        libssl.so.1.1 => /lib64/libssl.so.1.1 (0x00007ff838e17000)
        libcrypto.so.1.1 => /lib64/libcrypto.so.1.1 (0x00007ff838b29000)
        libc.so.6 => /lib64/libc.so.6 (0x00007ff83891f000)
        libz.so.1 => /lib64/libz.so.1 (0x00007ff838905000)
        /lib64/ld-linux-x86-64.so.2 (0x00007ff838f0b000)

$ strace -e openat python3.10 -c "from urllib.request import urlopen; urlopen('https://www.python.org')"
...
openat(AT_FDCWD, "/etc/pki/tls/openssl.cnf", O_RDONLY) = 3
openat(AT_FDCWD, "/etc/crypto-policies/back-ends/opensslcnf.config", O_RDONLY) = 4
openat(AT_FDCWD, "/etc/crypto-policies/back-ends/openssl.config", O_RDONLY) = 3
openat(AT_FDCWD, "/etc/pki/tls/cert.pem", O_RDONLY) = 3
...

Many thanks Christian, see the attached for the output of the commands on Python 3.9.10 and 3.10.2, along with a diff removing version numbers and memory addresses. 

I've run the commands on the Ubuntu distribution, we can also run the same for the Centos VM, if helpful.

There are a few differences in the outputs but nothing that appears obviously the cause.

pyenv uses default value for ./configure --with-ssl-default-suites. You have to use --with-ssl-default-suites=openssl so your build uses the system's crypto policy correctly.

Many thanks Christian, that resolved the issue! I really appreciate your efforts here.