Build Authorization Key for AWS Requests in C#

BuildAuthorizationKey.cs

/// <summary>
/// generates key to include in the "Authorization" request header
/// </summary>
/// <param name="accessKey">AWS access key</param>
/// <param name="secretKey">AWS secret key</param>
/// <param name="dateString">string included in the "x-amz-date" request header</param>
/// <returns>string to be used for signing request</returns>
static string BuildSignature(string accessKey, string secretKey, string dateString) {
    var hmacSha1 = new HMACSHA1(Encoding.UTF8.GetBytes(secretKey));
    var hashedDate = Convert.ToBase64String(hmacSha1.ComputeHash(Encoding.UTF8.GetBytes(dateString)));
    return string.Format("AWS {0}:{1}", accessKey, hashedDate);
}