diff --git a/auth/index.html b/auth/index.html
index f4f7cd2..c630845 100644
--- a/auth/index.html
+++ b/auth/index.html
@@ -268,12 +268,19 @@ <h2>Message log</h2>
           ) {
             throw new Error("cannot create uint8array from invalid hex string");
           }
+
           var buffer = new Uint8Array(
             hexString.match(/../g).map((h) => parseInt(h, 16))
           );
           if (!length) {
             return buffer;
           }
+          if (hexString.length / 2 > length) {
+            throw new Error(
+              "hex value cannot fit in a buffer of " + length + " byte(s)"
+            );
+          }
+
           var paddedBuffer = new Uint8Array(length);
           paddedBuffer.set(buffer, length - buffer.length);
           return paddedBuffer;
@@ -588,7 +595,7 @@ <h2>Message log</h2>
         /**
          * Converts a `BigInt` into a base64url encoded string
          * @param {BigInt} num
-         * @param {number} length: optional number of bytes contained in the resulting string
+         * @param {number} length: optional number of bytes contained in the intermediary buffer before encoding as base64url
          * @return {string}
          */
         var bigIntToBase64Url = function (num, length) {
@@ -990,6 +997,7 @@ <h2>Message log</h2>
           base64urlEncode,
           base64urlDecode,
           base58checkDecode,
+          bigIntToBase64Url,
           bigIntToHex,
           stringToBase64urlString,
           uint8arrayToHexString,
diff --git a/auth/index.test.js b/auth/index.test.js
index caa8141..53675ff 100644
--- a/auth/index.test.js
+++ b/auth/index.test.js
@@ -262,6 +262,10 @@ describe("TKHQ", () => {
     expect(TKHQ.uint8arrayFromHexString("01", 2).toString()).toEqual("0,1");
     // Happy path: if length parameter is omitted, do not pad the resulting buffer
     expect(TKHQ.uint8arrayFromHexString("01").toString()).toEqual("1");
+    // Error case: hex value cannot fit in desired length
+    expect(() => {
+      TKHQ.uint8arrayFromHexString("0100", 1).toString(); // the number 256 cannot fit into 1 byte
+    }).toThrow("hex value cannot fit in a buffer of 1 byte(s)");
   });
 
   it("contains bigIntToHex", () => {
@@ -275,6 +279,20 @@ describe("TKHQ", () => {
     }).toThrow("number cannot fit in a hex string of 2 characters");
   });
 
+  it("contains bigIntToBase64Url", () => {
+    expect(TKHQ.bigIntToBase64Url(BigInt(1))).toEqual("AQ");
+    expect(TKHQ.bigIntToBase64Url(BigInt(1), 2)).toEqual("AAE");
+
+    // extrapolate to larger numbers
+    expect(TKHQ.bigIntToBase64Url(BigInt(255))).toEqual("_w"); // max 1 byte
+    expect(TKHQ.bigIntToBase64Url(BigInt(255), 2)).toEqual("AP8"); // max 1 byte expressed in 2 bytes
+
+    // error case
+    expect(() => {
+      TKHQ.bigIntToBase64Url(BigInt(256), 1);
+    }).toThrow("hex value cannot fit in a buffer of 1 byte(s)");
+  });
+
   it("logs messages and sends messages up", async () => {
     // TODO: test logMessage / sendMessageUp
     expect(true).toBe(true);