diff --git a/include/basen/base58.hpp b/include/basen/base58.hpp
index aa9685d..551d46b 100644
--- a/include/basen/base58.hpp
+++ b/include/basen/base58.hpp
@@ -13,27 +13,27 @@ namespace base58
     extern const char digits[59];
     extern const int8_t map[256];
 
-    bool isValid(const char *str, uint64_t str_size) noexcept;
+    bool isValid(const char *str, size_t str_size) noexcept;
     bool isValid(std::string_view str) noexcept;
 
     /**
      * @throw std::overflow_error if if there is an overflow
      */
-    uint64_t sizeEncoded(std::span<const uint8_t> data) noexcept;
-    uint64_t sizeDecoded(std::string_view str) noexcept;
+    size_t sizeEncoded(std::span<const uint8_t> data) noexcept;
+    size_t sizeDecoded(std::string_view str) noexcept;
 
     /**
      * @return number of leading chars, which should be trimmed
      * @warning contain leading zeros, returns count of them
      */
-    uint64_t encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size) noexcept;
+    size_t encode(const uint8_t *data, size_t data_size, char *str, size_t str_size) noexcept;
     std::string encode(std::span<const uint8_t> data) noexcept;
 
     /**
      * @return number of leading chars, which should be trimmed
      * @warning contain leading zeros, returns count of them
      */
-    uint64_t decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size) noexcept;
+    size_t decode(const char *str, size_t str_size, uint8_t *data, size_t data_size) noexcept;
     std::vector<uint8_t> decode(std::string_view str) noexcept;
 
     /**
diff --git a/include/basen/base64.hpp b/include/basen/base64.hpp
index cd116b0..82a119e 100644
--- a/include/basen/base64.hpp
+++ b/include/basen/base64.hpp
@@ -10,20 +10,20 @@ namespace base64
     extern const char digits[65];
     extern const int8_t map[256];
 
-    bool isValid(const char *str, uint64_t str_size) noexcept;
+    bool isValid(const char *str, size_t str_size) noexcept;
     bool isValid(std::string_view str) noexcept;
 
     /**
      * @throw std::overflow_error if if there is an overflow
      */
-    uint64_t sizeEncoded(std::span<const uint8_t> data);
-    uint64_t sizeDecoded(std::string_view str) noexcept;
+    size_t sizeEncoded(std::span<const uint8_t> data);
+    size_t sizeDecoded(std::string_view str) noexcept;
 
     /**
      * @throw std::length_error if not enough allocated length
      * @warning contain leading zeros, returns count of them
      */
-    void encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size);
+    void encode(const uint8_t *data, size_t data_size, char *str, size_t str_size);
     std::string encode(std::span<const uint8_t> data) noexcept;
 
     /**
@@ -32,6 +32,6 @@ namespace base64
      * @throw std::logic_error if incorrect padding
      * @warning contain leading zeros, returns count of them
      */
-    void decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size);
+    void decode(const char *str, size_t str_size, uint8_t *data, size_t data_size);
     std::vector<uint8_t> decode(std::string_view str) noexcept;
 }
\ No newline at end of file
diff --git a/include/basen/baseN.hpp b/include/basen/baseN.hpp
index ced5997..6b49495 100644
--- a/include/basen/baseN.hpp
+++ b/include/basen/baseN.hpp
@@ -20,7 +20,7 @@ namespace baseN
      * @param map int8_t[256] array, where at an index equal to the value of the symbol is the index of this symbol in the digits array. -1 if there is no symbol
      * @return that string doesn't contain unnecessary symbols
      */
-    bool isValid(const char *str, uint64_t str_size, const int8_t *map) noexcept;
+    bool isValid(const char *str, size_t str_size, const int8_t *map) noexcept;
     /**
      * @param str string or string_view which you want to decode
      * @param map int8_t[256] array, where at an index equal to the value of the symbol is the index of this symbol in the digits array. -1 if there is no symbol
@@ -33,7 +33,7 @@ namespace baseN
      * @param base from 1 to 255
      * @return estimated size after encoding
      */
-    uint64_t sizeEncoded(std::span<const uint8_t> data, uint8_t base);
+    size_t sizeEncoded(std::span<const uint8_t> data, uint8_t base);
     /**
      * @param str string or string_view which you want to decode
      * @param base from 1 to 255
@@ -41,7 +41,7 @@ namespace baseN
      * @return estimated size after decoding
      * @throw std::overflow_error if if there is an overflow
      */
-    uint64_t sizeDecoded(std::string_view str, uint8_t base, const char *digits) noexcept;
+    size_t sizeDecoded(std::string_view str, uint8_t base, const char *digits) noexcept;
 
     /**
      * @param data [in] pointer to data which you want encode
@@ -61,7 +61,7 @@ namespace baseN
      * @return number of leading chars, which should be trimmed
      * @warning contain leading zeros, returns count of them
      */
-    uint64_t encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size, uint8_t base, const char *digits);
+    size_t encode(const uint8_t *data, size_t data_size, char *str, size_t str_size, uint8_t base, const char *digits);
     /**
      * @param data vector or span of data which you want to encode
      * @param base from 1 to 255
@@ -93,7 +93,7 @@ namespace baseN
      * @return number of leading chars, which should be trimmed
      * @warning contain leading zeros, returns count of them
      */
-    uint64_t decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size, uint8_t base, const char *digits, const int8_t *map);
+    size_t decode(const char *str, size_t str_size, uint8_t *data, size_t data_size, uint8_t base, const char *digits, const int8_t *map);
     /**
      * @param str string or string_view which you want to decode
      * @param base from 1 to 255
diff --git a/include/basen/hash/sha256.hpp b/include/basen/hash/sha256.hpp
index 279ecb5..e3a9d4c 100644
--- a/include/basen/hash/sha256.hpp
+++ b/include/basen/hash/sha256.hpp
@@ -6,6 +6,6 @@
 
 namespace hash
 {
-	void sha256(const uint8_t *data, uint64_t data_size, uint8_t *hash) noexcept;
+	void sha256(const uint8_t *data, size_t data_size, uint8_t *hash) noexcept;
 	std::vector<uint8_t> sha256(std::span<const uint8_t> data) noexcept;
 }
\ No newline at end of file
diff --git a/include/basen/hex.hpp b/include/basen/hex.hpp
index afd2a55..3288176 100644
--- a/include/basen/hex.hpp
+++ b/include/basen/hex.hpp
@@ -10,20 +10,20 @@ namespace hex
     extern const char digits[17];
     extern const int8_t map[256];
 
-    bool isValid(const char *str, uint64_t str_size) noexcept;
+    bool isValid(const char *str, size_t str_size) noexcept;
     bool isValid(std::string_view str) noexcept;
 
     /**
      * @throw std::overflow_error if if there is an overflow
      */
-    uint64_t sizeEncoded(std::span<const uint8_t> data);
-    uint64_t sizeDecoded(std::string_view str) noexcept;
+    size_t sizeEncoded(std::span<const uint8_t> data);
+    size_t sizeDecoded(std::string_view str) noexcept;
 
     /**
      * @throw std::length_error if not enough allocated length
      * @warning contain leading zeros, returns count of them
      */
-    void encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size);
+    void encode(const uint8_t *data, size_t data_size, char *str, size_t str_size);
     std::string encode(std::span<const uint8_t> data) noexcept;
 
     /**
@@ -32,6 +32,6 @@ namespace hex
      * @throw std::logic_error if str_size %2 != 0 (isn't hex)
      * @warning contain leading zeros, returns count of them
      */
-    void decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size);
+    void decode(const char *str, size_t str_size, uint8_t *data, size_t data_size);
     std::vector<uint8_t> decode(std::string_view str) noexcept;
 }
\ No newline at end of file
diff --git a/src/base58.cpp b/src/base58.cpp
index 190bac9..aa57532 100644
--- a/src/base58.cpp
+++ b/src/base58.cpp
@@ -27,7 +27,7 @@ namespace base58
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
         //
     };
-    bool isValid(const char *str, uint64_t str_size) noexcept
+    bool isValid(const char *str, size_t str_size) noexcept
     {
         return baseN::isValid(str, str_size, map);
     }
@@ -35,15 +35,15 @@ namespace base58
     {
         return baseN::isValid(str, map);
     }
-    uint64_t sizeEncoded(std::span<const uint8_t> data) noexcept
+    size_t sizeEncoded(std::span<const uint8_t> data) noexcept
     {
         return baseN::sizeEncoded(data, 58);
     }
-    uint64_t sizeDecoded(std::string_view str) noexcept
+    size_t sizeDecoded(std::string_view str) noexcept
     {
         return baseN::sizeDecoded(str, 58, digits);
     }
-    uint64_t encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size) noexcept
+    size_t encode(const uint8_t *data, size_t data_size, char *str, size_t str_size) noexcept
     {
         return baseN::encode(data, data_size, str, str_size, 58, digits);
     }
@@ -51,7 +51,7 @@ namespace base58
     {
         return baseN::encode(data, 58, digits);
     }
-    uint64_t decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size) noexcept
+    size_t decode(const char *str, size_t str_size, uint8_t *data, size_t data_size) noexcept
     {
         return baseN::decode(str, str_size, data, data_size, 58, digits, map);
     }
diff --git a/src/base64.cpp b/src/base64.cpp
index 0d20bb4..b1dc316 100644
--- a/src/base64.cpp
+++ b/src/base64.cpp
@@ -28,7 +28,7 @@ namespace base64
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
         //
     };
-    bool isValid(const char *str, uint64_t str_size) noexcept
+    bool isValid(const char *str, size_t str_size) noexcept
     {
         return base64::isValid(std::string_view(str, str_size));
     }
@@ -43,37 +43,37 @@ namespace base64
         }
         return baseN::isValid(sv, map);
     }
-    uint64_t sizeEncoded(std::span<const uint8_t> data)
+    size_t sizeEncoded(std::span<const uint8_t> data)
     {
-        uint64_t str_size = data.size() / 3;
-        if (str_size > std::numeric_limits<uint64_t>::max() / 4)
+        size_t str_size = data.size() / 3;
+        if (str_size > std::numeric_limits<size_t>::max() / 4)
         {
             throw std::overflow_error("base64::sizeEncoded: overflow");
         }
         str_size = str_size * 4 + (data.size() % 3 ? 4 : 0);
         return str_size;
     }
-    uint64_t sizeDecoded(std::string_view str) noexcept
+    size_t sizeDecoded(std::string_view str) noexcept
     {
         auto size = std::distance(str.begin(), std::find_if(str.rbegin(), str.rend(), [](char ch)
                                                             { return ch != '='; })
                                                    .base());
         return size / 4 * 3 + (size % 4 ? size % 4 - 1 : 0);
     }
-    void encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size)
+    void encode(const uint8_t *data, size_t data_size, char *str, size_t str_size)
     {
         if (str_size < base64::sizeEncoded(std::span<const uint8_t>(data, data_size)))
         {
             throw std::length_error("base64::encode: not enough allocated length");
         }
-        for (uint64_t i = 0; i < data_size / 3; i++)
+        for (size_t i = 0; i < data_size / 3; i++)
         {
             str[i * 4] = digits[data[i * 3] >> 2];
             str[i * 4 + 1] = digits[(data[i * 3] << 4 | data[i * 3 + 1] >> 4) & 0x3F];
             str[i * 4 + 2] = digits[(data[i * 3 + 1] << 2 | data[i * 3 + 2] >> 6) & 0x3F];
             str[i * 4 + 3] = digits[data[i * 3 + 2] & 0x3F];
         }
-        uint64_t last_idx = data_size / 3 * 4;
+        size_t last_idx = data_size / 3 * 4;
         switch (data_size % 3)
         {
         case 1:
@@ -98,7 +98,7 @@ namespace base64
         base64::encode(data.data(), data.size(), str.data(), str.size());
         return str;
     }
-    void decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size)
+    void decode(const char *str, size_t str_size, uint8_t *data, size_t data_size)
     {
         std::string_view sv(str, str_size);
         if (data_size < base64::sizeDecoded(sv))
@@ -122,7 +122,7 @@ namespace base64
             data[i * 3 + 1] = map[(int8_t)str[i * 4 + 1]] << 4 | map[(int8_t)str[i * 4 + 2]] >> 2;
             data[i * 3 + 2] = map[(int8_t)str[i * 4 + 2]] << 6 | map[(int8_t)str[i * 4 + 3]];
         }
-        uint64_t last_idx = size / 4 * 3;
+        size_t last_idx = size / 4 * 3;
         switch (size % 4)
         {
         case 2:
diff --git a/src/baseN.cpp b/src/baseN.cpp
index 17cc15d..5512f3a 100644
--- a/src/baseN.cpp
+++ b/src/baseN.cpp
@@ -21,7 +21,7 @@ namespace baseN
             map[(int8_t)digits[i]] = i;
         }
     }
-    bool isValid(const char *str, uint64_t str_size, const int8_t *map) noexcept
+    bool isValid(const char *str, size_t str_size, const int8_t *map) noexcept
     {
         return std::all_of(str, str + str_size, [map](char ch)
                            { return map[(int8_t)ch] != -1; });
@@ -30,25 +30,25 @@ namespace baseN
     {
         return baseN::isValid(str.data(), str.size(), map);
     }
-    uint64_t sizeEncoded(std::span<const uint8_t> data, uint8_t base)
+    size_t sizeEncoded(std::span<const uint8_t> data, uint8_t base)
     {
         std::span<const uint8_t> dv(std::find_if(data.begin(), data.end(), [](uint8_t item)
                                                  { return item != 0; }),
                                     data.end());
-        if (dv.size() > std::numeric_limits<uint64_t>::max() / log256)
+        if (dv.size() > std::numeric_limits<size_t>::max() / log256)
         {
             throw std::overflow_error("baseN::sizeEncoded: overflow");
         }
         return dv.size() * log256 / std::log(base) + 1 + (data.size() - dv.size());
     }
-    uint64_t sizeDecoded(std::string_view str, uint8_t base, const char *digits) noexcept
+    size_t sizeDecoded(std::string_view str, uint8_t base, const char *digits) noexcept
     {
         std::string_view sv(std::find_if(str.begin(), str.end(), [digits](uint8_t ch)
                                          { return ch != digits[0]; }),
                             str.end());
         return sv.size() * std::log(base) / log256 + 1 + (str.size() - sv.size());
     }
-    uint64_t encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size, uint8_t base, const char *digits)
+    size_t encode(const uint8_t *data, size_t data_size, char *str, size_t str_size, uint8_t base, const char *digits)
     {
         std::vector<uint8_t> dv(std::find_if(data, data + data_size, [](uint8_t item)
                                              { return item != 0; }),
@@ -86,7 +86,7 @@ namespace baseN
             }
             *sv_it++ = digits[div];
         }
-        for (uint64_t i = 0; i < data_size - dv.size() && sv_it < sv.rend(); i++)
+        for (size_t i = 0; i < data_size - dv.size() && sv_it < sv.rend(); i++)
         {
             *sv_it++ = digits[0];
         }
@@ -95,11 +95,11 @@ namespace baseN
     std::string encode(std::span<const uint8_t> data, uint8_t base, const char *digits) noexcept
     {
         std::string str(baseN::sizeEncoded(data, base), ' ');
-        uint64_t offset = baseN::encode(data.data(), data.size(), str.data(), str.size(), base, digits);
+        size_t offset = baseN::encode(data.data(), data.size(), str.data(), str.size(), base, digits);
         str.erase(str.begin(), str.begin() + offset);
         return str;
     }
-    uint64_t decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size, uint8_t base, const char *digits, const int8_t *map)
+    size_t decode(const char *str, size_t str_size, uint8_t *data, size_t data_size, uint8_t base, const char *digits, const int8_t *map)
     {
         std::string_view sv(std::find_if(str, str + str_size, [digits](char ch)
                                          { return ch != digits[0]; }),
@@ -135,7 +135,7 @@ namespace baseN
                 quo_it = dv.rbegin();
             }
         }
-        for (uint64_t i = 0; i < str_size - sv.size() && quo_it_last < dv.rend(); i++)
+        for (size_t i = 0; i < str_size - sv.size() && quo_it_last < dv.rend(); i++)
         {
             *quo_it_last++ = 0;
         }
@@ -144,7 +144,7 @@ namespace baseN
     std::vector<uint8_t> decode(std::string_view str, uint8_t base, const char *digits, const int8_t *map) noexcept
     {
         std::vector<uint8_t> data(baseN::sizeDecoded(str, base, digits));
-        uint64_t offset = baseN::decode(str.data(), str.size(), data.data(), data.size(), base, digits, map);
+        size_t offset = baseN::decode(str.data(), str.size(), data.data(), data.size(), base, digits, map);
         data.erase(data.begin(), data.begin() + offset);
         return data;
     }
diff --git a/src/hash/sha256.cpp b/src/hash/sha256.cpp
index 32d2b14..c423dc4 100644
--- a/src/hash/sha256.cpp
+++ b/src/hash/sha256.cpp
@@ -165,7 +165,7 @@ static void sha256_final(SHA256_CTX *ctx, uint8_t *hash)
 
 namespace hash
 {
-	void sha256(const uint8_t *data, uint64_t data_size, uint8_t *hash) noexcept
+	void sha256(const uint8_t *data, size_t data_size, uint8_t *hash) noexcept
 	{
 		SHA256_CTX ctx;
 		sha256_init(&ctx);
diff --git a/src/hex.cpp b/src/hex.cpp
index a5e4286..4008fd8 100644
--- a/src/hex.cpp
+++ b/src/hex.cpp
@@ -26,7 +26,7 @@ namespace hex
         -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
         //
     };
-    bool isValid(const char *str, uint64_t str_size) noexcept
+    bool isValid(const char *str, size_t str_size) noexcept
     {
         return baseN::isValid(str, str_size, map);
     }
@@ -34,25 +34,25 @@ namespace hex
     {
         return baseN::isValid(str, map);
     }
-    uint64_t sizeEncoded(std::span<const uint8_t> data)
+    size_t sizeEncoded(std::span<const uint8_t> data)
     {
-        if (data.size() > std::numeric_limits<uint64_t>::max() / 2)
+        if (data.size() > std::numeric_limits<size_t>::max() / 2)
         {
             throw std::overflow_error("hex::sizeEncoded: overflow");
         }
         return data.size() * 2;
     }
-    uint64_t sizeDecoded(std::string_view str) noexcept
+    size_t sizeDecoded(std::string_view str) noexcept
     {
         return str.size() / 2;
     }
-    void encode(const uint8_t *data, uint64_t data_size, char *str, uint64_t str_size)
+    void encode(const uint8_t *data, size_t data_size, char *str, size_t str_size)
     {
         if (str_size < hex::sizeEncoded(std::span<const uint8_t>(data, data_size)))
         {
             throw std::length_error("hex::encode: not enough allocated length");
         }
-        for (uint64_t i = 0; i < data_size; i++)
+        for (size_t i = 0; i < data_size; i++)
         {
             str[i * 2] = digits[data[i] >> 4];
             str[i * 2 + 1] = digits[data[i] & 0x0F];
@@ -64,7 +64,7 @@ namespace hex
         hex::encode(data.data(), data.size(), str.data(), str.size());
         return str;
     }
-    void decode(const char *str, uint64_t str_size, uint8_t *data, uint64_t data_size)
+    void decode(const char *str, size_t str_size, uint8_t *data, size_t data_size)
     {
         if (str_size % 2 != 0)
         {
@@ -78,7 +78,7 @@ namespace hex
         {
             throw std::logic_error("hex::decode: out of digits map");
         }
-        for (uint64_t i = 0; i * 2 < str_size; i++)
+        for (size_t i = 0; i * 2 < str_size; i++)
         {
             data[i] = map[(int8_t)str[i * 2]] << 4 | map[(int8_t)str[i * 2 + 1]];
         }
diff --git a/test/hash/test-sha256.cpp b/test/hash/test-sha256.cpp
index 0f2dc9b..2bc8c02 100644
--- a/test/hash/test-sha256.cpp
+++ b/test/hash/test-sha256.cpp
@@ -11,7 +11,7 @@ TEST(hash, sha256)
 TEST(hash, sha256_1e4)
 {
     std::vector<uint8_t> data(32);
-    for (uint64_t i = 0; i < 1e4; i++)
+    for (size_t i = 0; i < 1e4; i++)
     {
         sha256(data);
     }
diff --git a/test/test-base64.cpp b/test/test-base64.cpp
index 680d788..1b7aa3d 100644
--- a/test/test-base64.cpp
+++ b/test/test-base64.cpp
@@ -31,7 +31,7 @@ TEST(base64, encode)
 
     std::vector<uint8_t> data = {0x74, 0x65, 0x73, 0x74};
     std::string str = "";
-    EXPECT_THROW(encode(data.data(), std::numeric_limits<uint64_t>::max(), str.data(), str.size()), std::overflow_error);
+    EXPECT_THROW(encode(data.data(), std::numeric_limits<size_t>::max(), str.data(), str.size()), std::overflow_error);
     EXPECT_THROW(encode(data.data(), data.size(), str.data(), str.size()), std::length_error);
     EXPECT_NO_THROW(encode(data.data(), 0, str.data(), str.size()));
 }
diff --git a/test/test-baseN.cpp b/test/test-baseN.cpp
index 10a35d5..0ae97fd 100644
--- a/test/test-baseN.cpp
+++ b/test/test-baseN.cpp
@@ -26,7 +26,7 @@ TEST(baseN, isValid)
 }
 TEST(baseN, sizeEncoded)
 {
-    std::vector<std::pair<uint64_t, std::string>> tests = {
+    std::vector<std::pair<size_t, std::string>> tests = {
         {6, "12341234"},
         {5, "00000000"},
     };
@@ -35,7 +35,7 @@ TEST(baseN, sizeEncoded)
 }
 TEST(baseN, sizeDecoded)
 {
-    std::vector<std::pair<uint64_t, std::string>> tests = {
+    std::vector<std::pair<size_t, std::string>> tests = {
         {3, "qwer"},
         {5, "1111"},
     };
diff --git a/test/test-hex.cpp b/test/test-hex.cpp
index fb8dc79..30a739c 100644
--- a/test/test-hex.cpp
+++ b/test/test-hex.cpp
@@ -20,7 +20,7 @@ TEST(hex, encode)
     EXPECT_EQ("74657374", encode(data));
 
     std::string str = "";
-    EXPECT_THROW(encode(data.data(), std::numeric_limits<uint64_t>::max(), str.data(), str.size()), std::overflow_error);
+    EXPECT_THROW(encode(data.data(), std::numeric_limits<size_t>::max(), str.data(), str.size()), std::overflow_error);
     EXPECT_THROW(encode(data.data(), data.size(), str.data(), str.size()), std::length_error);
     EXPECT_NO_THROW(encode(data.data(), 0, str.data(), str.size()));
 }