Obsolete Encrypt / Decrypt with fOAEP

[vcsjones]

Closes #113616.

[Copilot]

Pull request overview

This pull request obsoletes the Encrypt and Decrypt methods on RSACryptoServiceProvider that accept a boolean parameter (fOAEP) for padding mode, as these methods implicitly use SHA-1 for OAEP padding which is now discouraged. Developers should use the overloads that accept RSAEncryptionPadding instead, which makes the hashing algorithm explicit.

Changes:

• Added [Obsolete] attributes with diagnostic ID SYSLIB0064 to RSACryptoServiceProvider.Encrypt(byte[], bool) and RSACryptoServiceProvider.Decrypt(byte[], bool) methods
• Refactored implementations to avoid mutual recursion: obsolete methods now delegate to the non-obsolete RSAEncryptionPadding overloads, while validation logic was moved from obsolete methods to the non-obsolete implementations
• Added SYSLIB0064 diagnostic ID, message, and documentation entry

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSACryptoServiceProvider.Windows.cs	Added obsolete attributes and refactored Windows implementation to move validation logic to non-obsolete methods
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSACryptoServiceProvider.Unix.cs	Added obsolete attributes and refactored Unix implementation to move validation logic to non-obsolete methods
src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/RSACryptoServiceProvider.NotSupported.cs	Added obsolete attributes to stub implementations for unsupported platforms
src/libraries/System.Security.Cryptography/ref/System.Security.Cryptography.cs	Updated reference assembly with obsolete attributes
src/libraries/Common/src/System/Obsoletions.cs	Added SYSLIB0064 diagnostic ID and message constants
docs/project/list-of-diagnostics.md	Added SYSLIB0064 to the diagnostic ID documentation table

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

[dotnet-policy-service]

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

When you commit this breaking change:

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Tagging @dotnet/compat for awareness of the breaking change.

[github-actions]

📋 Breaking Change Documentation Required

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Generated by Breaking Change Documentation Tool - 2026-03-06 19:13:04

[vcsjones]

Breaking changes doc: dotnet/docs#52108