diff --git a/bip39.c b/bip39.c
index 42ef82798..8d0fa1ee1 100644
--- a/bip39.c
+++ b/bip39.c
@@ -14,12 +14,9 @@ const char *mnemonic_generate(int strength)
 	if (strength % 32 || strength < 128 || strength > 256) {
 		return 0;
 	}
-	int i;
-	static uint32_t data[16];
-	for (i = 0; i < 16; i++) {
-		data[i] = random32();
-	}
-	return mnemonic_from_data((const uint8_t *)data, strength / 8);
+	static uint8_t data[32];
+	random_buffer(data, 32);
+	return mnemonic_from_data(data, strength / 8);
 }
 
 const char *mnemonic_from_data(const uint8_t *data, int len)
@@ -28,31 +25,23 @@ const char *mnemonic_from_data(const uint8_t *data, int len)
 		return 0;
 	}
 
-	int i, j;
-	char bits[256 + 8];
-	for (i = 0; i < len; i++) {
-		for (j = 0; j < 8; j++) {
-			bits[8 * i + j] = (data[i] & (1 << (7 - j))) > 0;
-		}
-	}
+	uint8_t bits[32 + 1];
+	memcpy(bits, data, len);
 
-	uint8_t hash[32];
-	sha256_Raw((const uint8_t *)data, len, hash);
-
-	char hlen = len / 4;
-	for (i = 0; i < hlen; i++) {
-		char c = (hash[0] & (1 << (7 - i))) > 0;
-		bits[8 * len + i] = c;
-	}
+	sha256_Raw(data, len, bits);
+	bits[len] = bits[0];
+	memcpy(bits, data, len);
 
 	int mlen = len * 3 / 4;
 	static char mnemo[24 * 10];
 
+	int i, j, idx;
 	char *p = mnemo;
 	for (i = 0; i < mlen; i++) {
-		int idx = 0;
+		idx = 0;
 		for (j = 0; j < 11; j++) {
-			idx += bits[i * 11 + j] << (10 - j);
+			idx <<= 1;
+			idx += (bits[(i * 11 + j) / 8] & (1 << (7 - ((i * 11 + j) % 8)))) > 0;
 		}
 		strcpy(p, wordlist[idx]);
 		p += strlen(wordlist[idx]);
@@ -65,9 +54,73 @@ const char *mnemonic_from_data(const uint8_t *data, int len)
 
 int mnemonic_check(const char *mnemonic)
 {
-	// TODO: add proper check
-	(void)mnemonic;
-	return 1;
+	if (!mnemonic) {
+		return 0;
+	}
+
+	uint32_t i, n;
+
+	i = 0; n = 0;
+	while (mnemonic[i]) {
+		if (mnemonic[i] == ' ') {
+			n++;
+		}
+		i++;
+	}
+	n++;
+	// check number of words
+	if (n != 12 && n != 18 && n != 24) {
+		return 0;
+	}
+
+	char current_word[10];
+	uint32_t j, k, ki, bi;
+	uint8_t bits[32 + 1];
+	memset(bits, 0, sizeof(bits));
+	i = 0; bi = 0;
+	while (mnemonic[i]) {
+		j = 0;
+		while (mnemonic[i] != ' ' && mnemonic[i] != 0) {
+			if (j >= sizeof(current_word)) {
+				return 0;
+			}
+			current_word[j] = mnemonic[i];
+			i++; j++;
+		}
+		current_word[j] = 0;
+		if (mnemonic[i] != 0) i++;
+		k = 0;
+		for (;;) {
+			if (!wordlist[k]) { // word not found
+				return 0;
+			}
+			if (strcmp(current_word, wordlist[k]) == 0) { // word found on index k
+				for (ki = 0; ki < 11; ki++) {
+					if (k & (1 << (10 - ki))) {
+						bits[bi / 8] |= 1 << (7 - (bi % 8));
+					}
+					bi++;
+				}
+				break;
+			}
+			k++;
+		}
+	}
+	if (bi != n * 11) {
+		return 0;
+	}
+	bits[32] = bits[n * 4 / 3];
+	sha256_Raw(bits, n * 4 / 3, bits);
+	if (n == 12) {
+		return (bits[0] & 0xF0) == (bits[32] & 0xF0); // compare first 4 bits
+	} else
+	if (n == 18) {
+		return (bits[0] & 0xFC) == (bits[32] & 0xFC); // compare first 6 bits
+	} else
+	if (n == 24) {
+		return bits[0] == bits[32]; // compare 8 bits
+	}
+	return 0;
 }
 
 void mnemonic_to_seed(const char *mnemonic, const char *passphrase, uint8_t seed[512 / 8], void (*progress_callback)(uint32_t current, uint32_t total))
diff --git a/rand.c b/rand.c
index fe6d724ad..20176d71e 100644
--- a/rand.c
+++ b/rand.c
@@ -27,12 +27,19 @@
 
 static FILE *f;
 
-void init_rand(void) {
+void init_rand(void)
+{
 	f = fopen("/dev/urandom", "r");
 }
 
-uint32_t random32(void) {
+uint32_t random32(void)
+{
 	uint32_t r;
 	fread(&r, 1, sizeof(r), f);
 	return r;
 }
+
+void random_buffer(uint8_t *buf, uint32_t len)
+{
+	fread(buf, 1, len, f);
+}
diff --git a/rand.h b/rand.h
index 2b72bde5e..fff02e260 100644
--- a/rand.h
+++ b/rand.h
@@ -28,5 +28,6 @@
 
 void init_rand(void);
 uint32_t random32(void);
+void random_buffer(uint8_t *buf, uint32_t len);
 
 #endif
diff --git a/tests.c b/tests.c
index ba2b4271d..7742466e4 100644
--- a/tests.c
+++ b/tests.c
@@ -458,6 +458,104 @@ START_TEST(test_mnemonic)
 }
 END_TEST
 
+START_TEST(test_mnemonic_check)
+{
+	static const char *vectors_ok[] = {
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",
+		"legal winner thank year wave sausage worth useful legal winner thank yellow",
+		"letter advice cage absurd amount doctor acoustic avoid letter advice cage above",
+		"zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong",
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon agent",
+		"legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will",
+		"letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always",
+		"zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo when",
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art",
+		"legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth title",
+		"letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless",
+		"zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo vote",
+		"jelly better achieve collect unaware mountain thought cargo oxygen act hood bridge",
+		"renew stay biology evidence goat welcome casual join adapt armor shuffle fault little machine walk stumble urge swap",
+		"dignity pass list indicate nasty swamp pool script soccer toe leaf photo multiply desk host tomato cradle drill spread actor shine dismiss champion exotic",
+		"afford alter spike radar gate glance object seek swamp infant panel yellow",
+		"indicate race push merry suffer human cruise dwarf pole review arch keep canvas theme poem divorce alter left",
+		"clutch control vehicle tonight unusual clog visa ice plunge glimpse recipe series open hour vintage deposit universe tip job dress radar refuse motion taste",
+		"turtle front uncle idea crush write shrug there lottery flower risk shell",
+		"kiss carry display unusual confirm curtain upgrade antique rotate hello void custom frequent obey nut hole price segment",
+		"exile ask congress lamp submit jacket era scheme attend cousin alcohol catch course end lucky hurt sentence oven short ball bird grab wing top",
+		"board flee heavy tunnel powder denial science ski answer betray cargo cat",
+		"board blade invite damage undo sun mimic interest slam gaze truly inherit resist great inject rocket museum chief",
+		"beyond stage sleep clip because twist token leaf atom beauty genius food business side grid unable middle armed observe pair crouch tonight away coconut",
+		0,
+	};
+	static const char *vectors_fail[] = {
+		"above abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",
+		"above winner thank year wave sausage worth useful legal winner thank yellow",
+		"above advice cage absurd amount doctor acoustic avoid letter advice cage above",
+		"above zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong",
+		"above abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon agent",
+		"above winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will",
+		"above advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always",
+		"above zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo when",
+		"above abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art",
+		"above winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth title",
+		"above advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless",
+		"above zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo vote",
+		"above better achieve collect unaware mountain thought cargo oxygen act hood bridge",
+		"above stay biology evidence goat welcome casual join adapt armor shuffle fault little machine walk stumble urge swap",
+		"above pass list indicate nasty swamp pool script soccer toe leaf photo multiply desk host tomato cradle drill spread actor shine dismiss champion exotic",
+		"above alter spike radar gate glance object seek swamp infant panel yellow",
+		"above race push merry suffer human cruise dwarf pole review arch keep canvas theme poem divorce alter left",
+		"above control vehicle tonight unusual clog visa ice plunge glimpse recipe series open hour vintage deposit universe tip job dress radar refuse motion taste",
+		"above front uncle idea crush write shrug there lottery flower risk shell",
+		"above carry display unusual confirm curtain upgrade antique rotate hello void custom frequent obey nut hole price segment",
+		"above ask congress lamp submit jacket era scheme attend cousin alcohol catch course end lucky hurt sentence oven short ball bird grab wing top",
+		"above flee heavy tunnel powder denial science ski answer betray cargo cat",
+		"above blade invite damage undo sun mimic interest slam gaze truly inherit resist great inject rocket museum chief",
+		"above stage sleep clip because twist token leaf atom beauty genius food business side grid unable middle armed observe pair crouch tonight away coconut",
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",
+		"winner thank year wave sausage worth useful legal winner thank yellow",
+		"advice cage absurd amount doctor acoustic avoid letter advice cage above",
+		"zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo wrong",
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon agent",
+		"winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal will",
+		"advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter always",
+		"zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo when",
+		"abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon art",
+		"winner thank year wave sausage worth useful legal winner thank year wave sausage worth useful legal winner thank year wave sausage worth title",
+		"advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic avoid letter advice cage absurd amount doctor acoustic bless",
+		"zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo zoo vote",
+		"better achieve collect unaware mountain thought cargo oxygen act hood bridge",
+		"stay biology evidence goat welcome casual join adapt armor shuffle fault little machine walk stumble urge swap",
+		"pass list indicate nasty swamp pool script soccer toe leaf photo multiply desk host tomato cradle drill spread actor shine dismiss champion exotic",
+		"alter spike radar gate glance object seek swamp infant panel yellow",
+		"race push merry suffer human cruise dwarf pole review arch keep canvas theme poem divorce alter left",
+		"control vehicle tonight unusual clog visa ice plunge glimpse recipe series open hour vintage deposit universe tip job dress radar refuse motion taste",
+		"front uncle idea crush write shrug there lottery flower risk shell",
+		"carry display unusual confirm curtain upgrade antique rotate hello void custom frequent obey nut hole price segment",
+		"ask congress lamp submit jacket era scheme attend cousin alcohol catch course end lucky hurt sentence oven short ball bird grab wing top",
+		"flee heavy tunnel powder denial science ski answer betray cargo cat",
+		"blade invite damage undo sun mimic interest slam gaze truly inherit resist great inject rocket museum chief",
+		"stage sleep clip because twist token leaf atom beauty genius food business side grid unable middle armed observe pair crouch tonight away coconut",
+		0,
+	};
+
+	const char **m;
+	int r;
+	m = vectors_ok;
+	while (*m) {
+		r = mnemonic_check(*m);
+		ck_assert_int_eq(r, 1);
+		m++;
+	}
+	m = vectors_fail;
+	while (*m) {
+		r = mnemonic_check(*m);
+		ck_assert_int_eq(r, 0);
+		m++;
+	}
+}
+END_TEST
+
 START_TEST(test_address)
 {
 	char address[35];
@@ -660,6 +758,7 @@ Suite *test_suite(void)
 
 	tc = tcase_create("bip39");
 	tcase_add_test(tc, test_mnemonic);
+	tcase_add_test(tc, test_mnemonic_check);
 	suite_add_tcase(s, tc);
 
 	return s;