make gosec linter pass (#3294)

* not related to linter: remove obsolete constants:
 - `Insecure` and `Secure` and type `Security` are not used anywhere

* not related to linter: update example

 - NewInsecure was deleted; change example to NewRemoteDB

* address: Binds to all network interfaces (gosec):

 - bind to localhost instead of 0.0.0.0
 - regenerate test key and cert for this purpose (was valid for ::) and
 otherwise we would see:
 transport: authentication handshake failed: x509: certificate is
 valid for ::, not 127.0.0.1\"

(used https://github.com/google/keytransparency/blob/master/scripts/gen_server_keys.sh
to regenerate certs)

* use sha256 in tests instead of md5; time difference is negligible

* nolint usage of math/rand in test and add comment on its import

 - crypto/rand is slower and we do not need sth more secure in tests

* enable linter in circle-ci

* another nolint math/rand in test

* replace another occurrence of md5

* consistent comment about importing math/rand

libs/db/remotedb/doc.go

@@ -11,7 +11,7 @@ remotedb's RemoteDB implements db.DB so can be used normally
 like other databases. One just has to explicitly connect to the
 remote database with a client setup such as:
 
-	client, err := remotedb.NewInsecure(addr)
+	client, err := remotedb.NewRemoteDB(addr, cert)
 	// Make sure to invoke InitRemote!
 	if err := client.InitRemote(&remotedb.Init{Name: "test-remote-db", Type: "leveldb"}); err != nil {
 	    log.Fatalf("Failed to initialize the remote db")

libs/db/remotedb/grpcdb/client.go

@@ -7,14 +7,6 @@ import (
 	protodb "github.com/tendermint/tendermint/libs/db/remotedb/proto"
 )
 
-// Security defines how the client will talk to the gRPC server.
-type Security uint
-
-const (
-	Insecure Security = iota
-	Secure
-)
-
 // NewClient creates a gRPC client connected to the bound gRPC server at serverAddr.
 // Use kind to set the level of security to either Secure or Insecure.
 func NewClient(serverAddr, serverCert string) (protodb.DBClient, error) {

libs/db/remotedb/remotedb_test.go

@@ -14,7 +14,7 @@ import (
 func TestRemoteDB(t *testing.T) {
 	cert := "test.crt"
 	key := "test.key"
-	ln, err := net.Listen("tcp", "0.0.0.0:0")
+	ln, err := net.Listen("tcp", "localhost:0")
 	require.Nil(t, err, "expecting a port to have been assigned on which we can listen")
 	srv, err := grpcdb.NewServer(cert, key)
 	require.Nil(t, err)

libs/db/remotedb/test.crt

@@ -1,25 +1,19 @@
 -----BEGIN CERTIFICATE-----
-MIIEQTCCAimgAwIBAgIRANqF1HD19i/uvQ3n62TAKTwwDQYJKoZIhvcNAQELBQAw
-GTEXMBUGA1UEAxMOdGVuZGVybWludC5jb20wHhcNMTgwNzAyMDMwNzMyWhcNMjAw
-MTAyMDMwNzMwWjANMQswCQYDVQQDEwI6OjCCASIwDQYJKoZIhvcNAQEBBQADggEP
-ADCCAQoCggEBAOuWUMCSzYJmvKU1vsouDTe7OxnPWO3oV0FjSH8vKYoi2zpZQX35
-dQDPtLDF2/v/ANZJ5pzMJR8yMMtEQ4tWxKuGzJw1ZgTgHtASPbj/M5fDnDO7Hqg4
-D09eLTkZAUfiBf6BzDyQIHn22CUexhaS70TbIT9AOAoOsGXMZz9d+iImKIm+gbzf
-pR52LNbBGesHWGjwIuGF4InstIMsKSwGv2DctzhWI+i/m5Goi3rd1V8z/lzUbsf1
-0uXqQcSfTyv3ee6YiCWj2W8vcdc5H+B6KzSlGjAR4sRcHTHOQJYO9BgA9evQ3qsJ
-Pp00iez13RdheJWPtbfUqQy4gdpu8HFeZx8CAwEAAaOBjzCBjDAOBgNVHQ8BAf8E
-BAMCA7gwHQYDVR0lBBYwFAYIKwYBBQUHAwEGCCsGAQUFBwMCMB0GA1UdDgQWBBRc
-XBo+bJILrLcJiGkTWeMPpXb1TDAfBgNVHSMEGDAWgBQqk1Xu65Ww7EBCROw4KLGw
-KuToaDAbBgNVHREEFDAShxAAAAAAAAAAAAAAAAAAAAAAMA0GCSqGSIb3DQEBCwUA
-A4ICAQAbGsIMhL8clczNmhGl9xZhmyNz6FbLq6g163x9LTgfvwHPt+7urthtd++O
-uy4Ut8zFurh/yk7eooPlzf8jO7QUJBAFVy4vj8IcsvpWbFa7cuEOIulbjIzyAm/v
-lgy7vUQ6xrWn8x8O9K1ww9z7wugwCyl22BD0wSHZKclJz++AwpL6vUVOD76IIuJO
-+S6bE6z26/0ndpundh2AkA++2eIleD6ygnTeTl0PWu6aGoCggBmos50f8KgYHZF/
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-381hyplQGPQOouEupCBxFcwa7oMYoGu20+1nLWYEqFcIXCeyH+s77MyteJSsseqL
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-f86Kp86M2elYnv3lJ3j2DE2ZTMpw+PA5ThYUnB+HVqYeeB2Y3ErRS8P1FOp1LBE8
-+eTz7yXQO5OM2wdYhNNL1zDri/41fHXi9b6337PZVqc39GM+N74x/O4Q7xEBiWgQ
-T0dT8SNwf55kv63MeZh63ImxFV0FNRkCteYLcJMle3ohIY4zyQ==
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+h/XgWjEt4DhpHwf/zuIK9XkJw0IaTWjFmoyKRoWW3q4bHzoKNxS9bXP117Tz7tn0
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+YWxob3N0hwQAAAAAhwR/AAABMA0GCSqGSIb3DQEBBQUAA4IBAQCe2A5gDc3jiZwT
+a5TJrc2J2KouqxB/PCddw5VY8jPsZJfsr9gxHi+Xa5g8p3oqmEOIlqM5BVhrZRUG
+RWHDmL+bCsuzMoA/vGHtHmUIwLeZQLWgT3kv12Dc8M9flNNjmXWxdMR9lOMwcL83
+F0CdElxSmaEbNvCIJBDetJJ7vMCqS2lnTLWurbH4ZGeGwvjzNgpgGCKwbyK/gU+j
+UXiTQbVvPQ3WWACDnfH6rg0TpxU9jOBkd+4/9tUrBG7UclQBfGULk3sObLO9kx4N
+8RxJmtp8jljIXVPX3udExI05pz039pAgvaeZWtP17QSbYcKF1jFtKo6ckrv2GKXX
+M5OXGXdw
 -----END CERTIFICATE-----

libs/db/remotedb/test.key

@@ -1,27 +1,27 @@
 -----BEGIN RSA PRIVATE KEY-----
-MIIEpgIBAAKCAQEA65ZQwJLNgma8pTW+yi4NN7s7Gc9Y7ehXQWNIfy8piiLbOllB
-ffl1AM+0sMXb+/8A1knmnMwlHzIwy0RDi1bEq4bMnDVmBOAe0BI9uP8zl8OcM7se
-qDgPT14tORkBR+IF/oHMPJAgefbYJR7GFpLvRNshP0A4Cg6wZcxnP136IiYoib6B
-vN+lHnYs1sEZ6wdYaPAi4YXgiey0gywpLAa/YNy3OFYj6L+bkaiLet3VXzP+XNRu
-x/XS5epBxJ9PK/d57piIJaPZby9x1zkf4HorNKUaMBHixFwdMc5Alg70GAD169De
-qwk+nTSJ7PXdF2F4lY+1t9SpDLiB2m7wcV5nHwIDAQABAoIBAQCB2/ilPgaUE8d2
-ldqWHa5hgw4/2uCdO04ll/GVUczm/PG1BxAnvYL2MIfcTSRGkrjGZjP9SDZKLONi
-mD1XKDv+hK5yiKi0lUnGzddCC0JILKYEieeLOGOQD0yERblEA13kfW20EIomUJ+y
-TnVIajQD03pPIDoDqTco1fQvpMDFYw5Q//UhH7VBC261GO1akvhT2Gqdb4aKLaYQ
-iDW9IEButL5cRKIJuRxToB/JbmPVEF7xIZtm0sf9dtYVOlBQLeID0uHXgaci0enc
-de6GMajmj7NFqc36ypb+Ct18fqEwQBYD+TSQdKs7/lMsAXwRjd5HW4RbYiMZyYnf
-Dxgh7QVBAoGBAP9aLLIUcIG7+gk1x7xd+8wRhfo+dhsungeCluSigI9AsfDr6dpR
-G9/0lEJH56noZZKQueACTmj7shmRB40xFFLc8w0IDRZCnofsl+Z15k9K84uFPA3W
-hdZH9nMieU/mRKdcUYK7pHGqbicHTaJQ5ydZ+xb2E+zYQHOzYpQacHv/AoGBAOwv
-TjDZSiassnAPYmmfcHtkUF4gf7PTpiZfH0hXHGAb0mJX4cXAoktAeDeHSi2tz3LW
-dAc0ReP8Pdf3uSNv7wkJ1KpNRxAhU5bhnDFmjRc7gMZknVOU+az2M+4yGOn/SOiJ
-I6uMHgQDS/VsI+N583n6gbGxVHbQfr9TOc4bLpThAoGBAKin0JmWMnEdzRnEMbZS
-hPrWIB2Wn794XNws/qjoQ+1aF60+xGhz5etXyYy1nWd1nZDekkZIf62LgKiuR8ST
-xA6u7MGQrcQkID06oWGQQZvhr1ZZm76wEBnl0ftdq66AMpwvt46XjReeL78LbdVl
-hidRoSwbQDHQ61EADH4xsFXVAoGBAISXqhXSZsZ/fU1b1avmTod3MYcmR4r07vnr
-vOwnu05ZUCrVm3IhSvtkHhlOYl5yjVuy+UByICp1mWJ9N/qlBFTWqAVTjOmJTBwQ
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-P69toyEBAoGBALh9YsqxHdYdS5WK9chzDfGlaTQ79jwN+gEzQuP1ooLF0JkMgh5W
-//2C6kCrgBsGTm1gfHAjEfC04ZDZLFbKLm56YVKUGL6JJNapm6e5kfiZGjbRKWAg
-ViCeRS2qQnVbH74GfHyimeTPDI9cJMiJfDDTPbfosqWSsPEcg2jfsySJ
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+x/kLjsYBaaJdt+H4rHeABTWfYDLHs9pDTTOK65mELGZE/rg6n6BWqMelP/qYKO8J
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+O7IIh8Cmb9TbdldgW+8ndZ4EQ3lfIS0zN3/7rWD34bs19JDYkRY=
 -----END RSA PRIVATE KEY-----