format counter function

Sources/CryptoSwift/BlockMode/CCM.swift

@@ -39,28 +39,65 @@ public struct CCM: BlockMode {
         return CBCModeWorker(blockSize: blockSize, iv: iv.slice, cipherOperation: cipherOperation)
     }
 
+//    // Apply the formatting function to (N, A, P) to produce blocks [B0, ..., Br]
+//    private func format(N: [UInt8], A: [UInt8], P: [UInt8]) throws -> [UInt8] {
+//        let block0 = try format(nonce: N, Q: 512, q: 3, t: 12, hasAssociatedData: false) // mock
+//        let ctr1 = try format(counter: 1, nonce: N, q: 3)
+//        return block0 + ctr1
+//    }
 
-    // Apply the formatting function to (N, A, P) to produce blocks [B0, ..., Br]
-    private func format(N: [UInt8], A: [UInt8], P: [UInt8]) throws -> [UInt8] {
-        let block0 = try formatNonce(N: N, Q: 512, q: 3, t: 12, hasAssociatedData: false) // mock
-        return []
+}
+
+struct CCMModeWorker: BlockModeWorker {
+    let cipherOperation: CipherOperationOnBlock
+    var blockSize: Int
+    let additionalBufferSize: Int = 0
+    private let iv: ArraySlice<UInt8>
+    private var prev: ArraySlice<UInt8>?
+
+    public enum Error: Swift.Error {
+        case invalidParameter
+    }
+
+
+    init(blockSize: Int, iv: ArraySlice<UInt8>, cipherOperation: @escaping CipherOperationOnBlock) {
+        self.blockSize = blockSize
+        self.iv = iv
+        self.cipherOperation = cipherOperation
+    }
+
+    mutating func encrypt(block plaintext: ArraySlice<UInt8>) -> Array<UInt8> {
+        guard let ciphertext = cipherOperation(xor(prev ?? iv, plaintext)) else {
+            return Array(plaintext)
+        }
+        prev = ciphertext.slice
+        return ciphertext
+    }
+
+    mutating func decrypt(block ciphertext: ArraySlice<UInt8>) -> Array<UInt8> {
+        guard let plaintext = cipherOperation(ciphertext) else {
+            return Array(ciphertext)
+        }
+        let result: Array<UInt8> = xor(prev ?? iv, plaintext)
+        prev = ciphertext
+        return result
     }
 
     // Q - octet length of P
     // q - octet length of Q. Maximum length (in octets) of payload. An element of {2,3,4,5,6,7,8}
     // t - octet length of T (MAC length). An element of {4,6,8,10,12,14,16}
-    private func formatNonce(N: [UInt8], Q: UInt32, q: UInt8, t: UInt8, hasAssociatedData: Bool) throws -> [UInt8] {
+    private func format(nonce N: [UInt8], Q: UInt32, q: UInt8, t: UInt8, hasAssociatedData: Bool) throws -> [UInt8] {
         var flags0: UInt8 = 0
 
         if hasAssociatedData {
-            // 6 bit
+            // 7 bit
             flags0 |= (1 << 6)
         }
 
-        // 5,4,3 is t in 3 bits
+        // 6,5,4 bit is t in 3 bits
         flags0 |= (((t-2)/2) & 0x07) << 3
 
-        // 2,1,0 is q in 3 bits
+        // 3,2,1 bit is q in 3 bits
         flags0 |= ((q-1) & 0x07) << 0
 
         var block0: [UInt8] = Array<UInt8>(repeating: 0, count: 16) // block[0]
@@ -80,35 +117,34 @@ public struct CCM: BlockMode {
 
         return block0
     }
-}
 
-struct CCMModeWorker: BlockModeWorker {
-    let cipherOperation: CipherOperationOnBlock
-    var blockSize: Int
-    let additionalBufferSize: Int = 0
-    private let iv: ArraySlice<UInt8>
-    private var prev: ArraySlice<UInt8>?
+    /// Formatting of the Counter Blocks. Ctr[i]
+    /// The counter generation function.
+    /// Q - octet length of P
+    /// q - octet length of Q. Maximum length (in octets) of payload. An element of {2,3,4,5,6,7,8}
+    private func format(counter i: Int, nonce N: [UInt8], q: UInt8) throws -> [UInt8] {
+        var flags0: UInt8 = 0
 
-    init(blockSize: Int, iv: ArraySlice<UInt8>, cipherOperation: @escaping CipherOperationOnBlock) {
-        self.blockSize = blockSize
-        self.iv = iv
-        self.cipherOperation = cipherOperation
-    }
+        // bit 8,7 is Reserved
+        // bit 4,5,6 shall be set to 0
+        // 3,2,1 bit is q in 3 bits
+        flags0 |= ((q-1) & 0x07) << 0
 
-    mutating func encrypt(block plaintext: ArraySlice<UInt8>) -> Array<UInt8> {
-        guard let ciphertext = cipherOperation(xor(prev ?? iv, plaintext)) else {
-            return Array(plaintext)
-        }
-        prev = ciphertext.slice
-        return ciphertext
-    }
+        var block = Array<UInt8>(repeating: 0, count: 16) // block[0]
+        block[0] = flags0
 
-    mutating func decrypt(block ciphertext: ArraySlice<UInt8>) -> Array<UInt8> {
-        guard let plaintext = cipherOperation(ciphertext) else {
-            return Array(ciphertext)
+        // N in 1...(15-q) octets, n = 15-q
+        // n is an element of {7,8,9,10,11,12,13}
+        let n = 15-Int(q)
+        guard (n + Int(q)) == 15 else {
+            // n+q == 15
+            throw Error.invalidParameter
         }
-        let result: Array<UInt8> = xor(prev ?? iv, plaintext)
-        prev = ciphertext
-        return result
+        block[1...n] = N[0...(n-1)]
+
+        // [i]8q in (16-q)...15 octets
+        block[(16-Int(q))...15] = i.bytes(totalBytes: Int(q)).slice
+
+        return block
     }
 }