Add method to detect multi-account mnemonic

Source/TonSwift/Mnemonic/Mnemonic.swift

@@ -117,6 +117,22 @@ public enum Mnemonic {
 
         return seed[0] == 0
     }
+
+    public static func isMultiAccountSeed(mnemonicArray: [String]) -> Bool {
+        let entropy = hmacSha512(phrase: "TON Keychain", password: mnemonicArray.joined(separator: " "))
+
+        // There is a collision propability with TON mnemonics 
+        if (isBasicSeed(entropy: mnemonicToEntropy(mnemonicArray: mnemonicArray, password: ""))) {
+          return false
+        }
+
+        let salt = "TON Keychain Version"
+        let saltData = Data(salt.utf8)
+        let seed = pbkdf2Sha512(phrase: entropy, salt: saltData, iterations: 1, keyLength: 64)
+
+        return seed[0] == 0
+    }
+
 
     public static func isPasswordSeed(entropy: Data) -> Bool {
         let salt = "TON fast seed version"

Tests/TonSwiftTests/Mnemonic/MnemonicTest.swift

@@ -19,5 +19,19 @@ final class MnemonicTest: XCTestCase {
         XCTAssertEqual(keyPair.publicKey.hexString, "34eb4b67d64f74d989ce2bc2e3dfddb7ed4cb0eec92f29fbecd05b1eabab0254")
         XCTAssertEqual(keyPair.privateKey.hexString, "c893fc0b676782a5c157ad8fddb389f75caba6eea1c198d8075a8a43afce70a934eb4b67d64f74d989ce2bc2e3dfddb7ed4cb0eec92f29fbecd05b1eabab0254")
     }
+
 
+  func testIsMultiAccountSeedMnemonic() throws {
+      let collisionMnemonic = "cluster notice abandon frost gospel boring element situate click mix vague replace imitate garment useful crater resource dose tenant theme foam ancient phrase slight".components(separatedBy: " ")
+
+      XCTAssertFalse(Mnemonic.isMultiAccountSeed(mnemonicArray: collisionMnemonic))
+
+      let multiAccountMnemonic = "execute peanut please demise thumb mango argue cloud reopen upset also dentist panic elite roast security pyramid extra boil execute lazy pledge notice check".components(separatedBy: " ")
+
+      XCTAssertTrue(Mnemonic.isMultiAccountSeed(mnemonicArray: multiAccountMnemonic))
+
+      let tonMnemonic = "item supply cover volcano satisfy window custom cupboard license dance record tissue gadget rural health blossom useless useless hungry brush grief stock reflect morning".components(separatedBy: " ")
+
+      XCTAssertFalse(Mnemonic.isMultiAccountSeed(mnemonicArray: tonMnemonic))
+  }
 }