diff --git a/tests/pkg/micro-ecc/Makefile b/tests/pkg/micro-ecc/Makefile
index cbc2d9d63d01..d0149a800cd9 100644
--- a/tests/pkg/micro-ecc/Makefile
+++ b/tests/pkg/micro-ecc/Makefile
@@ -1,6 +1,7 @@
 include ../Makefile.pkg_common
 
 USEMODULE += hashes
+USEMODULE += od
 USEPKG += micro-ecc
 
 include $(RIOTBASE)/Makefile.include
@@ -9,3 +10,6 @@ include $(RIOTBASE)/Makefile.include
 ifneq (,$(filter avr8_common,$(USEMODULE)))
   CFLAGS += -DTHREAD_STACKSIZE_MAIN=THREAD_STACKSIZE_LARGE
 endif
+
+# Access internal API for unit tests
+CFLAGS += -DuECC_ENABLE_VLI_API=1
diff --git a/tests/pkg/micro-ecc/main.c b/tests/pkg/micro-ecc/main.c
index 2941865ce132..229d9ede4e75 100644
--- a/tests/pkg/micro-ecc/main.c
+++ b/tests/pkg/micro-ecc/main.c
@@ -12,11 +12,43 @@
  *
  */
 
+#include <stdalign.h>
+#include <stdbool.h>
 #include <stdio.h>
-#include <string.h>
+
+#include "od.h"
 #include "test_utils/expect.h"
 #include "hashes/sha256.h"
 #include "uECC.h"
+#include "uECC_vli.h"
+
+/**
+ * @name    For access to mmod_fast for the unit tests, we sadly need to
+ *          copy-paste an internal struct definition.
+ * @{
+ */
+#define uECC_MAX_WORDS (32 / sizeof(uECC_word_t))
+struct uECC_Curve_t {
+    wordcount_t num_words;
+    wordcount_t num_bytes;
+    bitcount_t num_n_bits;
+    uECC_word_t p[uECC_MAX_WORDS];
+    uECC_word_t n[uECC_MAX_WORDS];
+    uECC_word_t G[uECC_MAX_WORDS * 2];
+    uECC_word_t b[uECC_MAX_WORDS];
+    void (*double_jacobian)(uECC_word_t * X1,
+                            uECC_word_t * Y1,
+                            uECC_word_t * Z1,
+                            uECC_Curve curve);
+#if uECC_SUPPORT_COMPRESSED_POINT
+    void (*mod_sqrt)(uECC_word_t *a, uECC_Curve curve);
+#endif
+    void (*x_side)(uECC_word_t *result, const uECC_word_t *x, uECC_Curve curve);
+#if (uECC_OPTIMIZATION_LEVEL > 0)
+    void (*mmod_fast)(uECC_word_t *result, uECC_word_t *product);
+#endif
+};
+/** @} */
 
 #define TESTROUNDS              (4)
 #define MAX_PUBLIC_KEY_SIZE     (64)
@@ -88,16 +120,242 @@ static void _finish_sha256(const uECC_HashContext *base, uint8_t *hash_result)
     sha256_final(&context->ctx, hash_result);
 }
 
+static bool _test_compare(const char *test_name, const void *got, const void *expected, size_t len)
+{
+    bool success = (0 == memcmp(got, expected, len));
+    static const char *fail_ok[] = { "[FAIL]", "[OK]  " };
+    printf("%s %s\n", fail_ok[success], test_name);
+    if (!success) {
+        puts("Got:");
+        od_hex_dump(got, len, 0);
+        puts("Expected:");
+        od_hex_dump(expected, len, 0);
+    }
+
+    return success;
+}
+
+static bool _test_uECC_vli_mult(void)
+{
+    const alignas(uECC_word_t) uint8_t input1[] = {
+        0x09, 0xB1, 0x2E, 0xA3,  0x85, 0xBB, 0xC7, 0x88,
+        0xFF, 0xD1, 0xC4, 0xEC,  0x2A, 0x6A, 0xF9, 0x7A,
+        0xE9, 0x7F, 0x39, 0x09,  0x86, 0x40, 0x94, 0x7E,
+        0xD3, 0x40, 0x04, 0xBC,  0xCC, 0xF9, 0xDD, 0xC3
+    };
+    const alignas(uECC_word_t) uint8_t input2[] = {
+        0x1F, 0xFE, 0x6A, 0x32,  0xDF, 0x35, 0xEC, 0x95,
+        0x2E, 0xF0, 0x24, 0x6D,  0x42, 0x0A, 0xA9, 0xE4,
+        0x4D, 0xE1, 0xAF, 0x49,  0xF9, 0x46, 0x9A, 0x0E,
+        0xCB, 0x25, 0x74, 0x8C,  0x69, 0x47, 0xEF, 0x9F
+    };
+    const alignas(uECC_word_t) uint8_t result_expected[] = {
+        0x17, 0x5E, 0x08, 0x26,  0xD7, 0x10, 0x12, 0xBD,
+        0xE0, 0x7C, 0x52, 0xCA,  0x12, 0xE7, 0x85, 0xE5,
+        0x7B, 0x95, 0xC5, 0x54,  0x60, 0x3F, 0x53, 0x9B,
+        0xB4, 0x8A, 0xAB, 0xFE,  0xEB, 0x50, 0x8F, 0x58,
+        0x5E, 0x12, 0x49, 0x86,  0x0A, 0x6D, 0xCA, 0x8F,
+        0x8A, 0x68, 0x02, 0x1E,  0x69, 0x15, 0xED, 0xEF,
+        0x21, 0x85, 0x65, 0x28,  0xBB, 0xDE, 0xAD, 0xC5,
+        0x75, 0xAB, 0xB3, 0xB0,  0x05, 0xF1, 0x5D, 0x7A
+    };
+    uint8_t alignas(uECC_word_t) result_got[sizeof(result_expected)];
+    uECC_vli_mult((void *)result_got, (void *)input1, (void *)input2, sizeof(input1) / sizeof(uECC_word_t));
+    return _test_compare("uECC_vli_mult()", result_got, result_expected, sizeof(result_expected));
+}
+
+static bool _test_uECC_vli_add(void)
+{
+    const alignas(uECC_word_t) uint8_t input1[] = {
+        0x59, 0x96, 0xC8, 0x96,  0x60, 0x03, 0x1A, 0xA1,
+        0xCF, 0x20, 0xC8, 0x2A,  0xC5, 0xC4, 0x93, 0x10,
+        0x54, 0xD7, 0x2E, 0x21,  0xDC, 0x99, 0xC0, 0x2A,
+        0xFC, 0x80, 0x8C, 0xA8,  0xD9, 0x63, 0xBE, 0x00
+    };
+    const alignas(uECC_word_t) uint8_t input2[] = {
+        0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+        0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x01, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xFF
+    };
+    const alignas(uECC_word_t) uint8_t result_expected[] = {
+        0x58, 0x96, 0xC8, 0x96, 0x60, 0x03, 0x1A, 0xA1,
+        0xCF, 0x20, 0xC8, 0x2A, 0xC6, 0xC4, 0x93, 0x10,
+        0x54, 0xD7, 0x2E, 0x21, 0xDC, 0x99, 0xC0, 0x2A,
+        0xFD, 0x80, 0x8C, 0xA8, 0xD8, 0x63, 0xBE, 0x00
+    };
+    const uECC_word_t carry_expected = 1;
+    uint8_t alignas(uECC_word_t) result_got[sizeof(result_expected)];
+    uECC_word_t carry_got = uECC_vli_add((void *)result_got, (void *)input1, (void *)input2, sizeof(input1)/sizeof(uECC_word_t));
+    return _test_compare("uECC_vli_add()", result_got, result_expected, sizeof(result_expected))
+        && _test_compare("uECC_vli_add() carry", &carry_got, &carry_expected, sizeof(carry_expected));
+}
+
+static bool _test_uECC_vli_sub(void)
+{
+    const alignas(uECC_word_t) uint8_t input1[] = {
+        0xD1, 0x09, 0x26, 0xCE, 0x2A, 0xE1, 0xE3, 0xBB,
+        0x99, 0xCF, 0x7A, 0x32, 0xE9, 0x38, 0x7D, 0xE2,
+        0x51, 0x8E, 0xCB, 0xE8, 0x68, 0xCE, 0xD7, 0x40,
+        0x3A, 0x22, 0x4B, 0x2D, 0x69, 0x99, 0x4D, 0x82
+    };
+    const alignas(uECC_word_t) uint8_t input2[] = {
+        0xBA, 0xC1, 0x36, 0xAA, 0xB4, 0x53, 0x80, 0x30,
+        0x36, 0xB7, 0xCF, 0x34, 0x58, 0x2D, 0x83, 0x56,
+        0xC9, 0xEB, 0x72, 0x0D, 0xC6, 0xCC, 0x46, 0x73,
+        0x1F, 0xAD, 0xE6, 0xEF, 0x96, 0x56, 0x4E, 0xAD
+    };
+    const alignas(uECC_word_t) uint8_t result_expected[] = {
+        0x17, 0x48, 0xEF, 0x23, 0x76, 0x8D, 0x63, 0x8B,
+        0x63, 0x18, 0xAB, 0xFD, 0x90, 0x0B, 0xFA, 0x8B,
+        0x88, 0xA2, 0x58, 0xDB, 0xA2, 0x01, 0x91, 0xCD,
+        0x1A, 0x75, 0x64, 0x3D, 0xD2, 0x42, 0xFF, 0xD4
+    };
+    const uECC_word_t borrow_expected = 1;
+    uint8_t alignas(uECC_word_t) result_got[sizeof(result_expected)];
+    uECC_word_t borrow_got = uECC_vli_sub((void *)result_got, (void *)input1, (void *)input2, sizeof(input1)/sizeof(uECC_word_t));
+    return _test_compare("uECC_vli_sub()", result_got, result_expected, sizeof(result_expected))
+        && _test_compare("uECC_vli_sub() borrow", &borrow_got, &borrow_expected, sizeof(borrow_expected));
+}
+
+static const alignas(uECC_word_t) uint8_t mmod_input[] = {
+    0xE8, 0x53, 0x32, 0xAB,  0x7B, 0x43, 0x11, 0x4C,
+    0xBA, 0x15, 0x85, 0x07,  0x06, 0x0B, 0x4D, 0x77,
+    0x1F, 0x4C, 0x00, 0x3B,  0xCB, 0xD3, 0x93, 0x5C,
+    0x9D, 0x0D, 0x59, 0xB0,  0xA8, 0xC8, 0x23, 0xE3,
+    0x2A, 0x25, 0x3B, 0xBD,  0x3B, 0xEF, 0xDE, 0x11,
+    0x84, 0x22, 0x5B, 0x73,  0x2D, 0x94, 0x01, 0x69,
+    0xCB, 0xE7, 0x8C, 0xBF,  0x4A, 0x0E, 0xEC, 0xC8,
+    0x8F, 0x2A, 0x70, 0x96,  0x98, 0x66, 0x85, 0x03
+};
+static const alignas(uECC_word_t) uint8_t mmod_result_expected[] = {
+    0x7B, 0xB3, 0x61, 0xF2,  0xFC, 0xCD, 0xDC, 0xAE,
+    0xF8, 0x2C, 0x00, 0x81,  0x43, 0x96, 0xB6, 0xBE,
+    0x1B, 0x51, 0x28, 0x5D,  0x67, 0xF5, 0x74, 0x42,
+    0x62, 0x54, 0x86, 0x74,  0xD5, 0x74, 0x19, 0x46
+};
+static bool _test_uECC_vli_mmod(void)
+{
+    static const alignas(uECC_word_t) uint8_t mod[] = {
+        0xFF, 0xFF, 0xFF, 0xFF,  0xFF, 0xFF, 0xFF, 0xFF,
+        0xFF, 0xFF, 0xFF, 0xFF,  0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00,
+        0x01, 0x00, 0x00, 0x00,  0xFF, 0xFF, 0xFF, 0xFF
+    };
+    uint8_t alignas(uECC_word_t) result_got[sizeof(mmod_result_expected)];
+    alignas(uECC_word_t) uint8_t product[sizeof(mmod_input)];
+    memcpy(product, mmod_input, sizeof(product));
+    uECC_vli_mmod((void *)result_got, (void *)product, (void *)mod, sizeof(mmod_result_expected) / sizeof(uECC_word_t));
+    return _test_compare("uECC_vli_mmod()", result_got, mmod_result_expected, sizeof(mmod_result_expected));
+}
+static bool _test_uECC_vli_mmod_fast(uECC_Curve curve)
+{
+    uint8_t alignas(uECC_word_t) result_got[sizeof(mmod_result_expected)];
+    alignas(uECC_word_t) uint8_t product[sizeof(mmod_input)];
+    memcpy(product, mmod_input, sizeof(product));
+    curve->mmod_fast((void *)result_got, (void *)product);
+    return _test_compare("curve->mmod_fast()", result_got, mmod_result_expected, sizeof(mmod_result_expected));
+}
+
+static bool _test_uECC_vli_modSquare_fast(const uECC_Curve curve)
+{
+    const alignas(uECC_word_t) uint8_t input[] = {
+        0xA9, 0x26, 0x99, 0xD4,  0xD1, 0x43, 0x3E, 0x22,
+        0x2A, 0xC3, 0x90, 0xE0,  0xF1, 0xE6, 0xEC, 0x1C,
+        0x97, 0xE7, 0x70, 0xB7,  0x79, 0xF3, 0x28, 0xB3,
+        0x30, 0xDB, 0xE1, 0x7C,  0x51, 0xCF, 0xEF, 0xFA,
+    };
+    const alignas(uECC_word_t) uint8_t result_expected[] = {
+    0x8B, 0x52, 0xAF, 0x3A,  0xD9, 0xA9, 0x88, 0xB4,
+    0x2F, 0x3C, 0xD5, 0xC5,  0x67, 0x3B, 0xBB, 0x64,
+    0xEC, 0xA5, 0x55, 0xCC,  0xFF, 0x6E, 0x6F, 0x02,
+    0xCF, 0x23, 0xBF, 0xFA,  0x74, 0x56, 0x8D, 0xC3
+    };
+    uint8_t alignas(uECC_word_t) result_got[sizeof(result_expected)];
+    uECC_vli_modSquare_fast((void *)result_got, (void *)input, curve);
+    return _test_compare("uECC_vli_modSquare_fast()", result_got, result_expected, sizeof(result_expected));
+}
+
+static bool _test_uECC_vli_modMult_fast(const uECC_Curve curve)
+{
+    const alignas(uECC_word_t) uint8_t input1[] = {
+        0x96, 0xC2, 0x98, 0xD8,  0x45, 0x39, 0xA1, 0xF4,
+        0xA0, 0x33, 0xEB, 0x2D,  0x81, 0x7D, 0x03, 0x77,
+        0xF2, 0x40, 0xA4, 0x63,  0xE5, 0xE6, 0xBC, 0xF8,
+        0x47, 0x42, 0x2C, 0xE1,  0xF2, 0xD1, 0x17, 0x6B
+    };
+    const alignas(uECC_word_t) uint8_t input2[] = {
+        0xC2, 0xF8, 0x5B, 0x35,  0x64, 0x8D, 0xD0, 0x25,
+        0x24, 0xE9, 0xAE, 0xB5,  0x04, 0x30, 0x57, 0x7C,
+        0x66, 0x9A, 0x8D, 0xE5,  0x7E, 0x26, 0x53, 0x78,
+        0x0A, 0xD3, 0xE2, 0xD5,  0xBD, 0x06, 0xA1, 0x11
+    };
+    const alignas(uECC_word_t) uint8_t result_expected[] = {
+        0xF9, 0xFD, 0xB6, 0x5C,  0x1B, 0x4F, 0x85, 0x35,
+        0x5C, 0x0D, 0x14, 0x47,  0x5B, 0x20, 0xD5, 0x9E,
+        0x35, 0x5C, 0x3E, 0xDE,  0xF9, 0x20, 0x37, 0x78,
+        0x34, 0x12, 0xD8, 0xF7,  0x80, 0xEF, 0x6E, 0x59
+    };
+    uint8_t alignas(uECC_word_t) result_got[sizeof(result_expected)];
+    uECC_vli_modMult_fast((void *)result_got, (void *)input1, (void *)input2, curve);
+    return _test_compare("uECC_vli_modMult_fast()", result_got, result_expected, sizeof(result_expected));
+}
+
+/**
+ * @brief   Runs internal functions with test vectors to not only see if
+ *          something broke, but also where
+ */
+static int _unit_tests(uECC_Curve curve)
+{
+    int errorc = 0;
+    puts("Unit Tests\n"
+         "==========\n");
+
+    if (!_test_uECC_vli_mult()) {
+        errorc++;
+    }
+
+    if (!_test_uECC_vli_add()) {
+        errorc++;
+    }
+
+    if (!_test_uECC_vli_sub()) {
+        errorc++;
+    }
+
+    if (!_test_uECC_vli_mmod()) {
+        errorc++;
+    }
+
+    if (!_test_uECC_vli_mmod_fast(curve)) {
+        errorc++;
+    }
+
+    if (!_test_uECC_vli_modSquare_fast(curve)) {
+        errorc++;
+    }
+
+    if (!_test_uECC_vli_modMult_fast(curve)) {
+        errorc++;
+    }
+
+    puts("");
+    return errorc;
+}
+
 int main(void)
 {
     printf("micro-ecc compiled!\n");
 
     const struct uECC_Curve_t *curve = uECC_secp256r1();
-    int errorc = 0;
 
     expect(uECC_curve_private_key_size(curve) <= MAX_CURVE_SIZE);
     expect(uECC_curve_public_key_size(curve) <= MAX_PUBLIC_KEY_SIZE);
 
+    int errorc = _unit_tests(curve);
+
+    puts("End to End Tests\n"
+         "================\n");
     printf("Testing %d random private key pairs and signature without using HWRNG\n", TESTROUNDS);
 
     for (int i = 0; i < TESTROUNDS; ++i) {