Set static thread count; add sanity check before encryption on example program

wrappers/keyDeriv.go

@@ -1,24 +1,21 @@
 package wrappers
 
 import (
-	"runtime"
-
 	"golang.org/x/crypto/argon2"
 )
 
 const (
 	// parameters for Argon2
-	argonTime   = 8          // set to pass 1-second test in dev environment
-	argonMemory = 384 * 1024 // 384 MB (target running comfortably on a Pi Zero/512 MB RAM)
+	argonTime    = 8          // set to pass 1-second test in dev environment
+	argonMemory  = 384 * 1024 // 384 MB (target running comfortably on a Pi Zero/512 MB RAM)
+	argonThreads = 32         // must use a static thread count for support across multiple devices
 
 	// general constants
 	keyLen   = 32 // 256 bits, key length for both algorithms
 	saltSize = 16 // 128 bits, recommended salt size for both algorithms
 )
 
-var argonThreads = uint8(runtime.NumCPU())
-
-// DeriveKey derives an encryption key from a passphrase using Argon2.
+// deriveKey derives an encryption key from a passphrase using Argon2.
 func deriveKey(passphrase []byte, salt []byte) []byte {
 	return argon2.IDKey(passphrase, salt, argonTime, argonMemory, argonThreads, keyLen)
 }