[#1] provide naming conventions

Signed-off-by: Ori Bruk <o.bruk@yadro.com>

cryptography/src/main/java/info/frostfs/sdk/Helper.java

@@ -0,0 +1,40 @@
+package info.frostfs.sdk;
+
+import com.google.protobuf.ByteString;
+import com.google.protobuf.Message;
+import org.bouncycastle.crypto.digests.RIPEMD160Digest;
+
+import java.math.BigInteger;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+public class Helper {
+
+    public static byte[] getRIPEMD160(byte[] value) {
+        var hash = new byte[20];
+        var digest = new RIPEMD160Digest();
+        digest.update(value, 0, value.length);
+        digest.doFinal(hash, 0);
+        return hash;
+    }
+
+    public static MessageDigest getSha256Instance() {
+        try {
+            return MessageDigest.getInstance("SHA-256");
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public static byte[] getSha256(byte[] value) {
+        return getSha256Instance().digest(value);
+    }
+
+    public static ByteString getSha256(Message value) {
+        return ByteString.copyFrom(getSha256(value.toByteArray()));
+    }
+
+    public static String getHexString(byte[] array) {
+        return String.format("%0" + (array.length << 1) + "x", new BigInteger(1, array));
+    }
+}