Bouncy Castle cryptography: .NET 10, OAEP, 2048-bit DSA, derived Blowfish key

[vladimir-pecanac-main]

Updates the sample for the Code Maze article "Bouncy Castle Cryptography in C# and .NET" (https://code-maze.com/csharp-bouncy-castle-cryptography/). Only authorization-dotnet/BouncyCastleCryptography changes.

Packages (re-queried on NuGet 2026-10-09; the re-query wins over the batch block):

• BouncyCastle.Cryptography 2.3.1 to 2.7.0 (latest, MIT, published 2026-07-30)
• Microsoft.NET.Test.Sdk 17.8.0 to 18.10.1 (batch block said 18.10.0)
• coverlet.collector 6.0.0 to 10.1.0 (batch block said 10.0.1)
• MSTest.TestAdapter and MSTest.TestFramework 3.1.1 to 4.5.1 (batch block said 4.4.0); MSTest kept, no test calls ThrowsException
• both projects net8.0 to net10.0

Code:

• RSA: OaepEncoding(new RsaEngine(), new Sha256Digest()) replaces Pkcs1Encoding.
• DSA: DsaParametersGenerator(new Sha256Digest()) with DsaParameterGenerationParameters(2048, 256, 80, random). The old Init(size, certainty, random) overload rejects anything above 1024 bits.
• Blowfish: the password goes through PBKDF2 (HMAC-SHA256, 600,000 iterations, random 16-byte salt) to a 128-bit key instead of being used as the key bytes. Encrypt and decrypt now take the salt. Static class, file-scoped namespace, redundant usings removed.
• AesDecrypt returns directly, matching the article snippet.
• Program.cs hashes the article input string and prints the DSA signature (it printed the Blowfish ciphertext under that label).
• Tests: "pasword" typo fixed, MD5 and SHA-256 known-answer tests added, unused out values discarded.

Local run (SDK 10.0.302, runtime 10.0.10): build 0 warnings 0 errors, 12 of 12 tests passed, dotnet list package --vulnerable --include-transitive clean on both projects.