[#1] provide naming conventions

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

cryptography/src/main/java/info/frostfs/sdk/Base58.java

@@ -0,0 +1,127 @@
+package info.frostfs.sdk;
+
+import java.util.Arrays;
+
+import static info.frostfs.sdk.ArrayHelper.concat;
+import static info.frostfs.sdk.Helper.getSha256;
+import static java.util.Objects.isNull;
+
+public class Base58 {
+    public static final char[] ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz".toCharArray();
+    private static final char ENCODED_ZERO = ALPHABET[0];
+    private static final int[] INDEXES = new int[128];
+
+    static {
+        Arrays.fill(INDEXES, -1);
+        for (int i = 0; i < ALPHABET.length; i++) {
+            INDEXES[ALPHABET[i]] = i;
+        }
+    }
+
+    public static byte[] base58CheckDecode(String input) {
+        if (isNull(input) || input.isEmpty()) {
+            throw new IllegalArgumentException("Input value is missing");
+        }
+
+        byte[] buffer = decode(input);
+        if (buffer.length < 4) {
+            throw new IllegalArgumentException();
+        }
+
+        byte[] decode = Arrays.copyOfRange(buffer, 0, buffer.length - 4);
+        byte[] checksum = getSha256(getSha256(decode));
+        if (!Arrays.equals(
+                Arrays.copyOfRange(buffer, buffer.length - 4, buffer.length),
+                Arrays.copyOfRange(checksum, 0, 4)
+        )) {
+            throw new IllegalArgumentException();
+        }
+
+        return decode;
+    }
+
+    public static String base58CheckEncode(byte[] data) {
+        byte[] checksum = getSha256(getSha256(data));
+        var buffer = concat(data, Arrays.copyOfRange(checksum, 0, 4));
+        var ret = encode(buffer);
+        return ret;
+    }
+
+    public static String encode(byte[] input) {
+        if (input.length == 0) {
+            return "";
+        }
+        // Count leading zeros.
+        int zeros = 0;
+        while (zeros < input.length && input[zeros] == 0) {
+            ++zeros;
+        }
+        // Convert base-256 digits to base-58 digits (plus conversion to ASCII characters)
+        input = Arrays.copyOf(input, input.length); // since we modify it in-place
+        char[] encoded = new char[input.length * 2]; // upper bound
+        int outputStart = encoded.length;
+        for (int inputStart = zeros; inputStart < input.length; ) {
+            encoded[--outputStart] = ALPHABET[divmod(input, inputStart, 256, 58)];
+            if (input[inputStart] == 0) {
+                ++inputStart; // optimization - skip leading zeros
+            }
+        }
+        // Preserve exactly as many leading encoded zeros in output as there were leading zeros in input.
+        while (outputStart < encoded.length && encoded[outputStart] == ENCODED_ZERO) {
+            ++outputStart;
+        }
+        while (--zeros >= 0) {
+            encoded[--outputStart] = ENCODED_ZERO;
+        }
+        // Return encoded string (including encoded leading zeros).
+        return new String(encoded, outputStart, encoded.length - outputStart);
+    }
+
+    public static byte[] decode(String input) {
+        if (input.isEmpty()) {
+            return new byte[0];
+        }
+        // Convert the base58-encoded ASCII chars to a base58 byte sequence (base58 digits).
+        byte[] input58 = new byte[input.length()];
+        for (int i = 0; i < input.length(); ++i) {
+            char c = input.charAt(i);
+            int digit = c < 128 ? INDEXES[c] : -1;
+            if (digit < 0) {
+                throw new IllegalArgumentException(String.format("Invalid character in Base58: 0x%04x", (int) c));
+            }
+            input58[i] = (byte) digit;
+        }
+        // Count leading zeros.
+        int zeros = 0;
+        while (zeros < input58.length && input58[zeros] == 0) {
+            ++zeros;
+        }
+        // Convert base-58 digits to base-256 digits.
+        byte[] decoded = new byte[input.length()];
+        int outputStart = decoded.length;
+        for (int inputStart = zeros; inputStart < input58.length; ) {
+            decoded[--outputStart] = divmod(input58, inputStart, 58, 256);
+            if (input58[inputStart] == 0) {
+                ++inputStart; // optimization - skip leading zeros
+            }
+        }
+        // Ignore extra leading zeroes that were added during the calculation.
+        while (outputStart < decoded.length && decoded[outputStart] == 0) {
+            ++outputStart;
+        }
+        // Return decoded data (including original number of leading zeros).
+        return Arrays.copyOfRange(decoded, outputStart - zeros, decoded.length);
+    }
+
+    private static byte divmod(byte[] number, int firstDigit, int base, int divisor) {
+        // this is just long division which accounts for the base of the input digits
+        int remainder = 0;
+        for (int i = firstDigit; i < number.length; i++) {
+            int digit = (int) number[i] & 0xFF;
+            int temp = remainder * base + digit;
+            number[i] = (byte) (temp / divisor);
+            remainder = temp % divisor;
+        }
+        return (byte) remainder;
+    }
+}