Fix linting

config/config.go

 	return len(c.AdTag) > 0
 }
 
-func (c *Config) SecretString() string {
+// BotSecretString returns secret string which should work with MTProxybot.
+func (c *Config) BotSecretString() string {
 	return hex.EncodeToString(c.Secret)
 }
 
-func (c *Config) BotSecretString() string {
-	secret := c.SecretString()
+// SecretString returns a secret in a form entered on the start of the
+// application.
+func (c *Config) SecretString() string {
+	secret := c.BotSecretString()
 	if c.SecureMode {
 		return "dd" + secret
 	}

wrappers/mtproto_intermediate_secure.go

 	"github.com/9seconds/mtg/mtproto"
 )
 
+// MTProtoIntermediateSecure is an extension of MTProtoIntermediate
+// mode which supports random paddings (socalled 'secure mode' or
+// 'dd-secrets').
 type MTProtoIntermediateSecure struct {
 	MTProtoIntermediate
 }
 	paddingLength := rand.Intn(4)
 	buf.Grow(4 + len(p) + paddingLength)
 
-	binary.Write(buf, binary.LittleEndian, uint32(len(p)+paddingLength))
+	binary.Write(buf, binary.LittleEndian, uint32(len(p)+paddingLength)) // nolint: errcheck
 	buf.Write(p)
 	buf.Write(make([]byte, paddingLength))
 
 	return len(p), err
 }
 
+// NewMTProtoIntermediateSecure create new instance of
+// MTProtoIntermediateSecure instance.
 func NewMTProtoIntermediateSecure(conn StreamReadWriteCloser, opts *mtproto.ConnectionOpts) PacketReadWriteCloser {
 	return &MTProtoIntermediateSecure{
 		MTProtoIntermediate: MTProtoIntermediate{