Fix test_cipher.rb in FIPS.

[junaruga]

This PR is to fix test_cipher.rb in FIPS.

I used the FIPS-approved algorithm AES-256-CBC instead of FIPS-not-approved algorithm DES-EDE3-CBC, also used the FIPS-approved algorithm SHA256 instead of FIPS-not-approved algorithm MD5 in some tests to pass the tests.

I confirmed the CI passed on my fork repository.
https://github.com/junaruga/ruby-openssl/actions/runs/20862608486

[rhenium]

Is OpenSSL::Cipher#pkcs5_keyivgen/EVP_BytesToKey() actually compliant if we use SHA-256? I suspect it isn't, but unifying on SHA-256 seems like a good idea.

[junaruga]

Originally I saw that the test_pkcs5_keyivgen failed as follows with OpenSSL.debug = true due to the DES-EDE3-CBC.

Error: test_pkcs5_keyivgen(OpenSSL::TestCipher): OpenSSL::Cipher::CipherError: EVP_CipherInit_ex
/home/jaruga/var/git/ruby/openssl/test/openssl/test_cipher.rb:37:in 'OpenSSL::Cipher#encrypt'
/home/jaruga/var/git/ruby/openssl/test/openssl/test_cipher.rb:37:in 'OpenSSL::TestCipher#test_pkcs5_keyivgen'
     34:     salt = "\x01" * 8
     35:     num = 2048
     36:     pt = "data to be encrypted"
  => 37:     cipher = OpenSSL::Cipher.new("DES-EDE3-CBC").encrypt
     38:     cipher.pkcs5_keyivgen(pass, salt, num, "MD5")
     39:     s1 = cipher.update(pt) << cipher.final
     40:-

However, when I ran the test_pkcs5_keyivgen with the cipher.pkcs5_keyivgen(pass, salt, num, "MD5") instead of the cipher.pkcs5_keyivgen(pass, salt, num, "SHA256"), the cipher.pkcs5_keyivgen(pass, salt, num, "MD5") still passed in the FIPS case. But later steps failed somehow.