openssl: OpenSSL 3.0.8: ed25519 a decode from and then encode to a pem file corrupts the key if fips+base provider is used

At an unit test in the OpenSSL Ruby binding (https://github.com/ruby/openssl), I see an FIPS mode specific issue related to ed25519 encryption. In my understanding, the program reads an ed25519 public key PEM file and convert it to something, then convert it to the PEM file again. The result of the final PEM file should be the same with the original PEM file. But the content is different with the OpenSSL 3.0.8 FIPS mode.

Fortunately I was able to prepare a reproducing program with only C language without Ruby. You can see it below.

The Ruby program

First, just let me share how the issue look like in the OpenSSL Ruby binding. I am testing it on the branch on my forked repository of the ruby/openssl, https://github.com/junaruga/openssl/tree/wip/fips-ed25519-report here.

In the following case with the ed25519 public key,

$ cat ed25519_pub.pem
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAPUAXw+hDiVqStwqnTRt+vJyYLM8uxJaMwM1V8Sr0Zgw=
-----END PUBLIC KEY-----

$ cat /etc/fedora-release 
Fedora release 37 (Thirty Seven)

$ ruby -v
ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-linux]

Non-FIPS mode

We expect that the following command returns the original ed25519_pub.pem’s content. And it works with the OpenSSL 3.0.8 non-FIPS mode.

$ LD_LIBRARY_PATH=/home/jaruga/.local/openssl-3.0.8-debug/lib/ \
  ruby -I lib -e "require 'openssl'; puts OpenSSL::PKey.read(File.read('ed25519_pub.pem')).public_to_pem"
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAPUAXw+hDiVqStwqnTRt+vJyYLM8uxJaMwM1V8Sr0Zgw=
-----END PUBLIC KEY-----

FIPS mode

$ LD_LIBRARY_PATH=/home/jaruga/.local/openssl-3.0.8-fips-debug/lib/ \
  OPENSSL_CONF=/home/jaruga/.local/openssl-3.0.8-fips-debug/ssl/openssl_fips.cnf \
  ruby -I lib -e "require 'openssl'; puts OpenSSL::PKey.read(File.read('ed25519_pub.pem')).public_to_pem"
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
-----END PUBLIC KEY-----

A reproducing program with C

Here is the program, https://github.com/junaruga/report-openssl-fips-ed25519.

$ cat ed25519_pub.pem
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAPUAXw+hDiVqStwqnTRt+vJyYLM8uxJaMwM1V8Sr0Zgw=
-----END PUBLIC KEY-----

$ gcc --version
gcc (GCC) 12.2.1 20221121 (Red Hat 12.2.1-4)
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ gcc -o ed25519 ed25519.c -lcrypto

Non-FIPS mode

The printed text on the last lines after [DEBUG] ossl_membio2str buf->data: are the same with the ed25519_pub.pem.

$ OPENSSL_CONF_INCLUDE=/home/jaruga/.local/openssl-3.0.8-debug/ssl \
  OPENSSL_MODULES=/home/jaruga/.local/openssl-3.0.8-debug/lib/ossl-modules \
  ./ed25519 ed25519_pub.pem
[DEBUG] Loaded providers:
  default
[DEBUG] Got a pkey! 0x24294e0
[DEBUG] It's held by the provider default
[DEBUG] ossl_membio2str buf->data:
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAPUAXw+hDiVqStwqnTRt+vJyYLM8uxJaMwM1V8Sr0Zgw=
-----END PUBLIC KEY-----

FIPS mode

The printed text is different from with the ed25519_pub.pem. Is this an expected behavior?

$ OPENSSL_CONF=/home/jaruga/.local/openssl-3.0.8-fips-debug/ssl/openssl_fips.cnf \
  OPENSSL_CONF_INCLUDE=/home/jaruga/.local/openssl-3.0.8-fips-debug/ssl \
  OPENSSL_MODULES=/home/jaruga/.local/openssl-3.0.8-fips-debug/lib/ossl-modules \
  ./ed25519 ed25519_pub.pem
[DEBUG] Loaded providers:
  fips
  base
[DEBUG] Got a pkey! 0x21476a0
[DEBUG] It's held by the provider fips
[DEBUG] ossl_membio2str buf->data:
-----BEGIN PUBLIC KEY-----
MCowBQYDK2VwAyEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
-----END PUBLIC KEY-----