Helper to convert byte array(blob) to hex string.

Hex.cs

using System;

namespace FipsTest
{
    public static class Hex
    {
        public const string HexDigits = "0123456789abcdef";

        private static char[] _lowerDigits;
        private static char[] _upperDigits;

        public static char[] LowerDigits => _lowerDigits ?? (_lowerDigits = GetHexDigits(true));
        public static char[] UpperDigits => _upperDigits ?? (_upperDigits = GetHexDigits(false));

        public static string ToHex(this byte[] data, bool toLowerCase = true) => ToHex(data, 0, data.Length, toLowerCase);

        public static string ToHex(this byte[] data, int start, int length, bool toLowerCase = true)
        {
            // https://stackoverflow.com/questions/9655181/how-to-convert-a-byte-array-to-a-hex-string-in-java/9855338#9855338
            // http://svn.apache.org/viewvc/commons/proper/codec/trunk/src/main/java/org/apache/commons/codec/binary/Hex.java?view=markup#l175

            if (start < 0 || start >= data.Length && start > 0)
                throw new ArgumentOutOfRangeException(nameof(start), "Value cannot be less that zero.");

            if (length < 0)
                throw new ArgumentOutOfRangeException(nameof(length), "Value must be positive.");

            if (start > data.Length - length)
                throw new ArgumentException("Destination array is not long enough to copy all the items in the collection. Check array index and length.");

            if (length == 0) return string.Empty;

            if (length > (int.MaxValue / 2))
                throw new ArgumentOutOfRangeException(nameof(length), $"The specified length exceeds the maximum value of {int.MaxValue / 2}.");

            var size = length * 2;
            var array = new char[size];
            var digits = toLowerCase ? LowerDigits : UpperDigits;
            for (int i = start, j = 0; j < size; i++)
            {
                array[j++] = digits[(0xF0 & data[i]) >> 4];
                array[j++] = digits[0x0F & data[i]];
            }

            return new string(array, 0, size);
        }

        private static char[] GetHexDigits(bool toLowerCase)
        {
            var source = HexDigits;
            return (toLowerCase ? source : source.ToUpperInvariant()).ToCharArray();
        }
    }
}