Extract and scan strings from unknown archive types (#467)

* Add string extraction functionality for unknown archive types, and scan these for secrets

Author: Copilot

pkg/archive/strings.go

@@ -0,0 +1,64 @@
+package archive
+
+import (
+	"bytes"
+)
+
+const (
+	// MinStringLength is the minimum length of a string to be considered printable
+	// This matches the default behavior of the Unix strings command
+	MinStringLength = 4
+)
+
+// ExtractPrintableStrings extracts printable ASCII strings from binary data.
+// It works similarly to the Unix 'strings' command, extracting sequences of printable
+// ASCII characters (and tabs, newlines, carriage returns) that are at least minLength
+// characters long. If minLength is 0, MinStringLength (4) is used as default.
+// Each extracted string is output on its own line, separated by newlines.
+func ExtractPrintableStrings(data []byte, minLength int) []byte {
+	if minLength <= 0 {
+		minLength = MinStringLength
+	}
+
+	var result bytes.Buffer
+	var currentString bytes.Buffer
+
+	for i := 0; i < len(data); i++ {
+		b := data[i]
+
+		if isPrintableByte(b) {
+			currentString.WriteByte(b)
+		} else {
+			if currentString.Len() >= minLength {
+				result.Write(currentString.Bytes())
+				result.WriteByte('\n')
+			}
+			currentString.Reset()
+		}
+	}
+
+	if currentString.Len() >= minLength {
+		result.Write(currentString.Bytes())
+		result.WriteByte('\n')
+	}
+
+	return result.Bytes()
+}
+
+// isPrintableByte checks if a byte represents a printable ASCII character.
+// This includes ASCII printable characters (32-126), tabs, newlines, and carriage returns.
+// We use byte-level checking to match the behavior of the Unix strings command,
+// which operates on bytes rather than UTF-8 runes.
+func isPrintableByte(b byte) bool {
+	// Accept tab, newline, and carriage return
+	if b == '\t' || b == '\n' || b == '\r' {
+		return true
+	}
+
+	// Accept ASCII printable characters (space through tilde)
+	if b >= 32 && b <= 126 {
+		return true
+	}
+
+	return false
+}