ateccx08: inttial implementation for ATECCx08

This working implementation for the ATECCx08 family of cryptgraphic processors
has random number generation and other needed supporting functions.

It also includes a sample of how to connect it to the Go crypto/rand package.

More cryptographic functions await a future interation.

Signed-off-by: deadprogram <ron@hybridgroup.com>

examples/ateccx08/random/rand.go

@@ -0,0 +1,52 @@
+// connects the Go crypto/rand package to the random number generation
+// on the ATECCx08 cryptographic processor.
+package main
+
+import (
+	"crypto/rand"
+	"errors"
+)
+
+var (
+	errNoATECC = errors.New("no ATECCx08")
+)
+
+func init() {
+	rand.Reader = &reader{}
+}
+
+type reader struct{}
+
+func (r *reader) Read(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return
+	}
+
+	if atecc == nil {
+		return 0, errNoATECC
+	}
+
+	if !atecc.IsLocked() {
+		panic("ATECCx08 is not locked and cannot produce random numbers!")
+	}
+
+	rnds, err := atecc.Random()
+	if err != nil {
+		return 0, err
+	}
+
+	for i := 0; i < len(b); i += 32 {
+		if i+32 > len(b) {
+			copy(b[i:], rnds[:(len(b)-i)])
+			break
+		}
+
+		copy(b[i:], rnds[:])
+		rnds, err = atecc.Random()
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	return len(b), nil
+}