IDX10603: The algorithm: 'HS256' requires the SecurityKey.KeySize to be greater than '128' bits. KeySize reported: '32'. Parameter name: key.KeySize

Question

I was just working with Asp.Net Core Web API, and implementing Authentication. And I am calling this API from an Angular Application. But I am always getting an error as below.

IDX10603: The algorithm: 'HS256' requires the SecurityKey.KeySize to be greater than '128' bits. KeySize reported: '32'. Parameter name: key.KeySize

Below is my code for ConfigureServices in Startup.cs file.

public IServiceProvider ConfigureServices(IServiceCollection services)
            {
                services.AddDbContext<APIContext>(option => option.UseInMemoryDatabase("AngularApp"));

                services.AddCors(options => options.AddPolicy("Cors", builder =>
                {
                    builder.AllowAnyOrigin().
                    AllowAnyMethod().
                    AllowAnyHeader();
                }
                ));

                var signinKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("Secret phase"));

                services.AddAuthentication(options =>
                {
                    options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
                    options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
                }).AddJwtBearer(cfg =>
                {
                    cfg.RequireHttpsMetadata = false;
                    cfg.SaveToken = true;
                    cfg.TokenValidationParameters = new Microsoft.IdentityModel.Tokens.TokenValidationParameters()
                    {
                        IssuerSigningKey = signinKey,
                        ValidateAudience = false,
                        ValidateIssuer = false,
                        ValidateLifetime = false,
                        ValidateIssuerSigningKey = true,
                        ValidateActor = false,
                        ClockSkew = TimeSpan.Zero
                    };
                });
                services.AddMvc();

                var serviceProvider = services.BuildServiceProvider();
                return serviceProvider;
            }

And I am using JwtPackagein my controller as follows.

JwtPackage CreateJwtToken(User usr)
        {
            var signinKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("this is my custom Secret key for authnetication"));
            var signInCredentials = new SigningCredentials(signinKey, SecurityAlgorithms.HmacSha256);
            var claims = new Claim[] {
                new Claim(JwtRegisteredClaimNames.Sub,usr.Id)
            };
            var jwt = new JwtSecurityToken(claims: claims, signingCredentials: signInCredentials);
            var encodedJwt = new JwtSecurityTokenHandler().WriteToken(jwt);
            return new JwtPackage() { FirstName = usr.FirstName, Token = encodedJwt };
        }

Can you please help me to fix this issue? Thank you.

Answer 1

Ah, it was my mistake, a simple one. I was not providing enough characters for the secret key name.

I changed my signinkey to this one,

var signinKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("this is my custom Secret key for authentication"));

from,

var signinKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("Secret phase"));

That solved my issue, as the HmacSha256 in the line SigningCredentials(signinKey, SecurityAlgorithms.HmacSha256)should be greater than 128 bits. In short, just use a long string as the key.