diff --git a/common/codex32.c b/common/codex32.c
index 781223d7a..afaee90e1 100644
--- a/common/codex32.c
+++ b/common/codex32.c
@@ -16,6 +16,145 @@
 #include <string.h>
 #include <time.h>
 
+struct checksum_engine {
+	u8 generator[15];
+	u8 residue[15];
+	u8 target[15];
+	size_t len;
+};
+
+static const struct checksum_engine initial_engine_csum[] = {
+	/* Short Codex32 Engine */
+	{
+		{
+			25, 27, 17, 8, 0, 25,
+			25, 25,	31, 27, 24, 16,
+			16,
+		},
+		{
+			0, 0, 0, 0, 0, 0,
+			0, 0, 0, 0, 0, 0,
+			1,
+		},
+		{
+			16, 25,	24, 3, 25, 11,
+			16, 23,	29, 3, 25, 17,
+			10,
+		},
+		13,
+	},
+	/* Long Codex32 Engine */
+	{
+		{
+			15, 10, 25, 26,	9, 25,
+			21, 6,	23, 21,	6, 5,
+			22, 4, 23
+		},
+		{
+			0, 0, 0, 0, 0, 0,
+			0, 0, 0, 0, 0, 0,
+			0, 0, 1
+		},
+		{
+			16, 25,	24, 3, 25, 11,
+			16, 23,	29, 3, 25, 17,
+			10, 25,	6
+		},
+		15,
+	}
+};
+
+static const uint8_t logi[32] =
+{
+     0,  0,  1, 14,  2, 28, 15, 22,
+     3,  5, 29, 26, 16,  7, 23, 11,
+     4, 25,  6, 10, 30, 13, 27, 21,
+    17, 18,  8, 19, 24,  9, 12, 20,
+};
+
+static const uint8_t log_inv[31] =
+{
+     1,  2,  4,  8, 16,  9, 18, 13,
+    26, 29, 19, 15, 30, 21,  3,  6,
+    12, 24, 25, 27, 31, 23,  7, 14,
+    28, 17, 11, 22,  5, 10, 20,
+};
+
+static void addition_gf32(uint8_t *x, uint8_t y)
+{
+	*x = *x ^ y;
+	return;
+}
+
+static void multiply_gf32(uint8_t *x, uint8_t y)
+{
+	if (*x == 0 || y == 0) {
+		*x = 0;
+	} else {
+		*x = log_inv[(logi[*x] + logi[y]) % 31];
+	}
+	return;
+}
+
+/* Helper to input a single field element in the checksum engine. */
+static void input_fe(const u8 *generator, u8 *residue, uint8_t e, int len)
+{
+	size_t res_len = len;
+	u8 xn = residue[0];
+
+	for(size_t i = 1; i < res_len; i++) {
+		residue[i - 1] = residue[i];
+	}
+
+	residue[res_len - 1] = e;
+
+	for(size_t i = 0; i < res_len; i++) {
+		u8 x = generator[i];
+		multiply_gf32(&x, xn);
+		addition_gf32(&residue[i], x);
+	}
+}
+
+/* Helper to input the HRP of codex32 string into the checksum engine */
+static void input_hrp(const u8 *generator, u8 *residue, const char *hrp, int len)
+{
+	size_t i = 0;
+	for (i = 0; i < strlen(hrp); i++) {
+		input_fe(generator, residue, tolower(hrp[i]) >> 5, len);
+	}
+	input_fe(generator, residue, tolower(hrp[i]) >> 0, len);
+	for (i = 0; i < strlen(hrp); i++) {
+		input_fe(generator, residue, tolower(hrp[i]) & 0x1f, len);
+	}
+	return;
+}
+
+/* Helper to input data strong of codex32 into the checksum engine. */
+static void input_data_str(u8 *generator, u8 *residue, const char *datastr, int len)
+{
+	size_t i = 0;
+
+	for (i = 0; i < strlen(datastr); i++) {
+		input_fe(generator, residue, bech32_charset_rev[(int)datastr[i]], len);
+	}
+
+	return;
+}
+
+/* Helper to verify codex32 checksum */
+static bool checksum_verify (const char *hrp, const char *codex_datastr, bool codexl)
+{
+	struct checksum_engine engine =  initial_engine_csum[codexl];
+
+	input_hrp((&engine)->generator, (&engine)->residue ,hrp, engine.len);
+	input_data_str((&engine)->generator, (&engine)->residue, codex_datastr, engine.len);
+
+	if (memcmp((&engine)->target, (&engine)->residue,
+		     engine.len) != 0) {
+			return false;
+	}
+	return true;
+}
 
 /* Helper to sanity check the codex32 string parts */
 static char *sanity_check (const tal_t *ctx,
@@ -185,6 +324,10 @@ struct codex32 *codex32_decode(const tal_t *ctx,
 		checksum_len = 13;
 	}
 
+	if(!checksum_verify(hrp, codex_datastr, parts->codexl)) {
+		*fail = tal_fmt(ctx, "Invalid checksum!");
+		return tal_free(parts);
+	}
 
 	parts->hrp = hrp;
 	parts->threshold = *pull_front_bytes(parts, &codex_datastr, 1) - '0';
diff --git a/common/codex32.h b/common/codex32.h
index 4936b1f2b..237a2010d 100644
--- a/common/codex32.h
+++ b/common/codex32.h
@@ -18,6 +18,7 @@ struct codex32 {
 	const char *share_idx;
 	const char *payload;
 	const char *checksum;
+	/* True if it is a codex32 long string, otherwise false. */
 	bool codexl;
 	codex32_encoding type;
 };