Added EME and EMSA PKCS1v15 Padding Schemes

Author: btoms20

Sources/CryptoSwift/PKCS/PKCS1v15.swift

@@ -0,0 +1,92 @@
+//
+//  CryptoSwift
+//
+//  Copyright (C) 2014-2021 Marcin Krzyżanowski <[email protected]>
+//  This software is provided 'as-is', without any express or implied warranty.
+//
+//  In no event will the authors be held liable for any damages arising from the use of this software.
+//
+//  Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
+//
+//  - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
+//  - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+//  - This notice may not be removed or altered from any source or binary distribution.
+//
+
+//  PKCS is a group of public-key cryptography standards devised
+//  and published by RSA Security Inc, starting in the early 1990s.
+//
+
+/// EMSA PKCS1 v1.5 Padding Scheme
+///
+/// The EMSA Version of the PKCS1 v1.5 padding scheme is **deterministic** (it pads the messages contents with 255 value bytes)
+/// ```
+/// // The returned structure
+/// // - PS is the applied padding
+/// // - M is your original Message
+/// EM = 0x00 || 0x01 || PS || 0x00 || M.
+/// ```
+/// - Note: This Padding scheme is intended to be used for encoding RSA Signatures
+struct EMSAPKCS1v15Padding: PaddingProtocol {
+
+  init() {
+  }
+
+  @inlinable
+  func add(to bytes: Array<UInt8>, blockSize: Int) -> Array<UInt8> {
+    var r = blockSize - ((bytes.count + 3) % blockSize)
+    if r <= 0 { r = blockSize - 3 }
+
+    return [0x00, 0x01] + Array<UInt8>(repeating: 0xFF, count: r) + [0x00] + bytes
+  }
+
+  @inlinable
+  func remove(from bytes: Array<UInt8>, blockSize _: Int?) -> Array<UInt8> {
+    assert(!bytes.isEmpty, "Need bytes to remove padding")
+
+    assert(bytes.prefix(2) == [0x00, 0x01], "Invalid padding prefix")
+
+    guard let paddingLength = bytes.dropFirst(2).firstIndex(of: 0x00) else { return bytes }
+
+    guard (paddingLength + 1) <= bytes.count else { return bytes }
+
+    return Array(bytes[(paddingLength + 1)...])
+  }
+}
+
+/// EME PKCS1 v1.5 Padding Scheme
+///
+/// The EME Version of the PKCS1 v1.5 padding scheme is **non deterministic** (it pads the messages contents with psuedo-random bytes)
+/// ```
+/// // The returned structure
+/// // - PS is the applied padding
+/// // - M is your original Message
+/// EM = 0x00 || 0x02 || PS || 0x00 || M.
+/// ```
+/// - Note: This Padding scheme is intended to be used for encoding messages before RSA Encryption
+struct EMEPKCS1v15Padding: PaddingProtocol {
+
+  init() {
+  }
+
+  @inlinable
+  func add(to bytes: Array<UInt8>, blockSize: Int) -> Array<UInt8> {
+    var r = blockSize - ((bytes.count + 3) % blockSize)
+    if r <= 0 { r = blockSize - 3 }
+
+    return [0x00, 0x02] + (0..<r).map { _ in UInt8.random(in: 1...UInt8.max) } + [0x00] + bytes
+  }
+
+  @inlinable
+  func remove(from bytes: Array<UInt8>, blockSize _: Int?) -> Array<UInt8> {
+    assert(!bytes.isEmpty, "Need bytes to remove padding")
+
+    assert(bytes.prefix(2) == [0x00, 0x02], "Invalid padding prefix")
+
+    guard let paddingLength = bytes.dropFirst(2).firstIndex(of: 0x00) else { return bytes }
+
+    guard (paddingLength + 1) <= bytes.count else { return bytes }
+
+    return Array(bytes[(paddingLength + 1)...])
+  }
+}