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This seems like it should easily documented but I am unable to find.

My c# code does this to create a pfx file.

X509Certificate2 cert = store.Certificates.Find(X509FindType.FindByThumbprint, thumbPrint, false);
                    File.WriteAllBytes("certFile.pfx", cert.Export(X509ContentType.Pfx, password));

The class X509Certificate2 is from System.Security.Cryptography.X509Certificates which appears to be a built-in .NET library.

I would like to know what encryption algorithm is being used to protect the pfx file. I want to confirm whether it is AES256 or not, but I can't seem to find this information anywhere.

I tried running this OpenSSL command on my "certFile.pfx" file. I had trouble with password so I used "no password" command line. Does this mean that the pfx file is encrypted using TripleDES?!

OpenSSL> pkcs12 -info -in C:\certFile.pfx -nomacver -noout -passin pass:unknown
MAC: sha1, Iteration 2000
MAC length: 20, salt length: 20
PKCS7 Data
Shrouded Keybag: pbeWithSHA1And3-KeyTripleDES-CBC, Iteration 2000
PKCS7 Encrypted data: pbeWithSHA1And3-KeyTripleDES-CBC, Iteration 2000
Error outputting keys and certificates
89924:error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad decrypt:crypto\evp\evp_enc.c:570:
89924:error:23077074:PKCS12 routines:PKCS12_pbe_crypt:pkcs12 cipherfinal error:crypto\pkcs12\p12_decr.c:63:
89924:error:2306A075:PKCS12 routines:PKCS12_item_decrypt_d2i:pkcs12 pbe crypt error:crypto\pkcs12\p12_decr.c:94:
error in pkcs12
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  • Thanks for the edit!
    – schroeder
    Jul 9 '20 at 14:38
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Does this mean that the pfx file is encrypted using TripleDES?

Yep. PFX/PKCS#12 files originally used an extended version of PBES1 (Password-Based Encryption Scheme 1) which added support for DES3-EDE (aka TripleDES aka 3DES). Support for PBES2 (which automatically brought in AES) has since been added, but for Windows that was only done in Windows 10 (IIRC).

Since everyone who could read PFXes could read them with PBES1/PKCS12-3DES, but not everyone can read them with PBES2/AES, "everyone" still defaults to producing files with 3DES.

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    More exactly, 'everyone' still uses pbepkcs12-3/3des for the privatekey(s), and same-rc2-40 for the certbag, which latter is easily breakable and provides no real security but makes using the file less convenient. Jul 9 '20 at 2:34

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