Fix a couple of issues

Author: ptoffy

Sources/Bcrypt/Base64.swift

@@ -1,3 +1,7 @@
+enum Base64Error: Error {
+    case invalidCharacter
+}
+
 @usableFromInline
 struct Base64 {
     @usableFromInline
@@ -74,7 +78,7 @@ struct Base64 {
     }
 
     @usableFromInline
-    static func decode(_ s: [UInt8], count maxolen: Int) -> [UInt8] {
+    static func decode(_ s: [UInt8], count maxolen: Int) throws(Base64Error) -> [UInt8] {
         var off = 0
         var olen = 0
         var result = [UInt8](repeating: 0, count: maxolen)
@@ -91,7 +95,7 @@ struct Base64 {
             c2 = char64(of: s[off])
             off &+= 1
             if c1 == UInt8.max || c2 == UInt8.max {
-                break
+                throw .invalidCharacter
             }
 
             o = c1 &<< 2
@@ -106,7 +110,7 @@ struct Base64 {
             off &+= 1
 
             if c3 == UInt8.max {
-                break
+                throw .invalidCharacter
             }
 
             o = (c2 & 0x0f) &<< 4

Sources/Bcrypt/Hasher.swift

@@ -48,7 +48,16 @@ extension Bcrypt {
             throw BcryptError.invalidSaltLength
         }
 
-        let cSalt = Base64.decode(salt, count: Self.maxSalt)
+        let cSalt: [UInt8]
+        do {
+            cSalt = try Base64.decode(salt, count: Self.maxSalt)
+        } catch {
+            throw BcryptError.invalidSalt
+        }
+
+        guard cSalt.count == 16 else {
+            throw BcryptError.invalidSalt
+        }
 
         guard password.count > 0 else {
             throw BcryptError.emptyPassword

Sources/Bcrypt/Verifier.swift

@@ -49,7 +49,7 @@ extension Bcrypt {
     guard a.count == b.count else { return false }
     var areEqual: UInt8 = 0
     var i = a.count - 1
-    while i != 0 {
+    while i >= 0 {
         areEqual |= a[i] ^ b[i]
         i -= 1
     }