diff --git a/src/wp_rsa_sig.c b/src/wp_rsa_sig.c
index 7639edf5..e237eba5 100644
--- a/src/wp_rsa_sig.c
+++ b/src/wp_rsa_sig.c
@@ -469,7 +469,9 @@ static int wp_rsa_signverify_init(wp_RsaSigCtx* ctx, wp_Rsa* rsa,
         ctx->saltLen = RSA_PSS_SALTLEN_AUTO;
 
         if (wp_rsa_get_type(ctx->rsa) == RSA_FLAG_TYPE_RSA) {
-            ctx->padMode = RSA_PKCS1_PADDING;
+            if (ctx->padMode != RSA_X931_PADDING) {
+                ctx->padMode = RSA_PKCS1_PADDING;
+            }
         }
         else {
             char* mdName;
@@ -651,6 +653,56 @@ static int wp_rsa_sign_pss(wp_RsaSigCtx* ctx, unsigned char* sig,
     return ok;
 }
 
+/**
+ * Add X9.31 padding to the input buffer, placing the result in the output
+ * buffer.
+ *
+ * @param  to       [out]  Buffer to store padded result.
+ * @param  toLen    [in]   Length of "to" buffer.
+ * @param  from     [in]   Input buffer.
+ * @param  fromLen  [in]   Length of input buffer.
+ * @returns  1 on success and 0 on failure.
+ */
+static int wp_add_x931_padding(unsigned char* to, size_t toLen,
+                               const unsigned char* from, size_t fromLen)
+{
+    int ok = 1;
+    int padBytes;
+
+    if (to == NULL || from == NULL) {
+        WOLFPROV_ERROR_MSG(WP_LOG_PK, "Bad argument.");
+        ok = 0;
+    }
+    else {
+        /* Need at least two bytes for trailer and header. */
+        padBytes = (int)(toLen - fromLen - 2);
+        if (padBytes < 0) {
+            WOLFPROV_ERROR_MSG(WP_LOG_PK, "Output buffer too small.");
+            ok = 0;
+        }
+    }
+
+    if (ok == 1) {
+        if (padBytes == 0) {
+            to[0] = 0x6A;
+        }
+        else {
+            to[0] = 0x6B;
+            if (padBytes > 1) {
+                XMEMSET(&to[1], 0xBB, padBytes - 1);
+            }
+            to[padBytes] = 0xBA;
+        }
+
+        XMEMCPY(&to[padBytes + 1], from, fromLen);
+        to[toLen - 1] = 0xCC;
+    }
+
+    WOLFPROV_LEAVE(WP_LOG_PK, __FILE__ ":" WOLFPROV_STRINGIZE(__LINE__), ok);
+
+    return ok;
+}
+
 /**
  * Sign the data using RSA without padding.
  *
@@ -691,6 +743,134 @@ static int wp_rsa_sign_no_pad(wp_RsaSigCtx* ctx, unsigned char* sig,
     return ok;
 }
 
+static int wp_rsa_get_x931_hash_code(enum wc_HashType hash) {
+    int ret = 0;
+
+    if (hash == WC_HASH_TYPE_SHA) {
+        ret = 0x33;
+    }
+    else if (hash == WC_HASH_TYPE_SHA256) {
+        ret = 0x34;
+    }
+    else if (hash == WC_HASH_TYPE_SHA384) {
+        ret = 0x36;
+    }
+    else if (hash == WC_HASH_TYPE_SHA512) {
+        ret = 0x35;
+    }
+
+    return ret;
+}
+
+/**
+ * Sign the data using RSA with X931 padding.
+ *
+ * @param [in, out] ctx      RSA signature context object.
+ * @param [out]     sig      Buffer to hold signature.
+ * @param [out]     sigLen   Length of signature data in bytes.
+ * @param [in]      sigSize  Size of signature buffer in bytes.
+ * @param [in]      tbs      Data to be signed.
+ * @param [in]      tbsLen   Length of data to be signed in bytes.
+ * @return  1 on success.
+ * @return  0 on failure.
+ */
+static int wp_rsa_sign_x931(wp_RsaSigCtx* ctx, unsigned char* sig,
+    size_t* sigLen, size_t sigSize, const unsigned char* tbs, size_t tbsLen)
+{
+    int ok = 1;
+    int paddedSz = 0;
+    unsigned char *padded = NULL;
+    unsigned char *tbuf = NULL;
+    int rc = 0;
+    mp_int toMp;
+    mp_int nMinusTo;
+
+    paddedSz = wc_RsaEncryptSize(wp_rsa_get_key(ctx->rsa));
+    if (paddedSz <= 0) {
+        ok = 0;
+    }
+    if (ok) {
+        tbuf = (unsigned char *)OPENSSL_malloc(paddedSz);
+        if (tbuf == NULL) {
+            ok = 0;
+        }
+    }
+    if (ok) {
+        padded = (unsigned char *)OPENSSL_malloc(paddedSz);
+        if (padded == NULL) {
+            ok = 0;
+        }
+    }
+    if (ok) {
+        XMEMCPY(tbuf, tbs, tbsLen);
+        tbuf[tbsLen] = wp_rsa_get_x931_hash_code(
+    #if LIBWOLFSSL_VERSION_HEX >= 0x05007004
+            ctx->hash.type
+    #else
+            ctx->hashType
+    #endif
+        );
+    }
+    if (ok) {
+        if (wp_add_x931_padding(padded, paddedSz, tbuf, tbsLen + 1) != 1) {
+            ok = 0;
+        }
+    }
+    if (ok) {
+        word32 len = (word32)sigSize;
+
+        PRIVATE_KEY_UNLOCK();
+        rc = wc_RsaDirect(padded, paddedSz, sig, &len,
+            wp_rsa_get_key(ctx->rsa), RSA_PRIVATE_ENCRYPT, &ctx->rng);
+        PRIVATE_KEY_LOCK();
+        if (rc < 0) {
+            ok = 0;
+        }
+        else {
+            *sigLen = rc;
+        }
+    }
+    if (padded != NULL) {
+        OPENSSL_free(padded);
+    }
+    if (tbuf != NULL) {
+        OPENSSL_free(tbuf);
+    }
+    if (ok) {
+        rc = mp_init_multi(&toMp, &nMinusTo, NULL, NULL, NULL, NULL);
+        if (rc != MP_OKAY) {
+            ok = 0;
+        }
+    }
+    if (ok) {
+        rc = mp_read_unsigned_bin(&toMp, sig, *sigLen);
+        if (rc != MP_OKAY) {
+            ok = 0;
+        }
+    }
+    if (ok) {
+        /*
+         * X9.31 specifies, "The signature is either the result
+         * or its complement to n, whichever is smaller."
+         */
+        rc = mp_sub(&(wp_rsa_get_key(ctx->rsa)->n), &toMp, &nMinusTo);
+        if (rc != MP_OKAY) {
+            ok = 0;
+        }
+        else if (mp_cmp(&toMp, &nMinusTo) == MP_GT) {
+            rc = mp_to_unsigned_bin(&nMinusTo, sig);
+            if (rc != MP_OKAY) {
+                ok = 0;
+            }
+        }
+    }
+    mp_free(&toMp);
+    mp_free(&nMinusTo);
+
+    WOLFPROV_LEAVE(WP_LOG_PK, __FILE__ ":" WOLFPROV_STRINGIZE(__LINE__), ok);
+    return ok;
+}
+
 /**
  * Sign the data using an RSA key.
  *
@@ -733,6 +913,9 @@ static int wp_rsa_sign(wp_RsaSigCtx* ctx, unsigned char* sig, size_t* sigLen,
         else if (ctx->padMode == RSA_NO_PADDING) {
             ok = wp_rsa_sign_no_pad(ctx, sig, sigLen, sigSize, tbs, tbsLen);
         }
+        else if (ctx->padMode == RSA_X931_PADDING) {
+            ok = wp_rsa_sign_x931(ctx, sig, sigLen, sigSize, tbs, tbsLen);
+        }
         else {
             ok = 0;
         }
@@ -929,6 +1112,166 @@ static int wp_rsa_verify_no_pad(wp_RsaSigCtx* ctx, const unsigned char* sig,
     return ok;
 }
 
+/**
+ * Remove X9.31 padding from the input buffer, placing the result in the output
+ * buffer.
+ *
+ * @param  to       [out]  Pointer to buffer holding unpadded result. This
+ *                         buffer will be allocated by this function if *to is
+ *                         NULL.
+ * @param  from     [in]   Input buffer.
+ * @param  fromLen  [in]   Length of input buffer.
+ * @returns  Length of unpadded result on success and -1 on failure.
+ */
+static int wp_remove_x931_padding(unsigned char** to, const unsigned char* from,
+                                  size_t fromLen)
+{
+    int ret = -1;
+    int ok = 1;
+    size_t idx = 0;
+    size_t numCopy = 0;
+
+    if (to == NULL || from == NULL || fromLen < 2) {
+        ok = 0;
+    }
+    else {
+        if (from[fromLen - 1] != 0xCC) {
+            ok = 0;
+        }
+
+        if (from[idx] == 0x6B) {
+            while (++idx < fromLen && from[idx] == 0xBB) {}
+
+            if (idx == fromLen || from[idx] != 0xBA) {
+                ok = 0;
+            }
+        }
+        else if (from[idx] != 0x6A) {
+            ok = 0;
+        }
+    }
+
+    if (ok) {
+        ++idx;
+        numCopy = fromLen - idx - 1;
+        if (numCopy > 0) {
+            if (*to == NULL) {
+                *to = (unsigned char*)OPENSSL_malloc(numCopy);
+                if (*to == NULL) {
+                    ok = 0;
+                }
+            }
+            if (ok){
+                XMEMCPY(*to, from + idx, numCopy);
+            }
+        }
+    }
+
+    if (ok) {
+        ret = (int)numCopy;
+    }
+
+    WOLFPROV_LEAVE(WP_LOG_PK, __FILE__ ":" WOLFPROV_STRINGIZE(__LINE__), ret);
+    return ret;
+}
+
+/**
+ * Verify an RSA X931 padded signature.
+ *
+ * @param [in] ctx           RSA signature context object.
+ * @param [in] sig           Signature data.
+ * @param [in] sigLen        Length of signature data in bytes.
+ * @param [in] tbs           Data to be signed.
+ * @param [in] tbsLen        Length of data to be signed in bytes.
+ * @param [in] decryptedSig  Buffer to hold decrypted signature.
+ * @return  1 on success.
+ * @return  0 on failure.
+ */
+static int wp_rsa_verify_x931(wp_RsaSigCtx* ctx, const unsigned char* sig,
+    size_t sigLen, const unsigned char* tbs, size_t tbsLen,
+    unsigned char* decryptedSig)
+{
+    int ok = 1;
+    int rc;
+    word32 len = (word32)sigLen;
+    unsigned char* unpadded = NULL;
+    mp_int toMp;
+    mp_int nMinusTo;
+
+    rc = wc_RsaDirect((byte*)sig, (word32)sigLen, decryptedSig, &len,
+        wp_rsa_get_key(ctx->rsa), RSA_PUBLIC_DECRYPT, &ctx->rng);
+    if (rc < 0) {
+        ok = 0;
+    }
+    if (ok) {
+        /*
+         * X9.31 specifies, "If e is odd, then
+         *   - If RR = 12 mod 16, then IR = RR ;
+         *   - If n - RR = 12 mod 16, then IR = n - RR ;"
+         * RR is "to" and IR is the value to unpad in the next
+         * step. Taking "to" mod 16 is the same as just checking the
+         * lower 4 bits of "to."
+         */
+        if ((decryptedSig[sigLen-1] & 0x0F) != 12) {
+            rc = mp_init_multi(&toMp, &nMinusTo, NULL, NULL, NULL, NULL);
+            if (rc != MP_OKAY) {
+                ok = 0;
+            }
+            if (ok) {
+                rc = mp_read_unsigned_bin(&toMp, decryptedSig, (int)sigLen);
+                if (rc != MP_OKAY) {
+                    ok = 0;
+                }
+                else {
+                    rc = mp_sub(&(wp_rsa_get_key(ctx->rsa)->n), &toMp, &nMinusTo);
+                    if (rc != MP_OKAY) {
+                        ok = 0;
+                    }
+                    else {
+                        rc = mp_to_unsigned_bin(&nMinusTo, decryptedSig);
+                        if (rc != MP_OKAY) {
+                            ok = 0;
+                        }
+                    }
+                }
+            }
+            mp_free(&toMp);
+            mp_free(&nMinusTo);
+        }
+    }
+    if (ok) {
+        rc = wp_remove_x931_padding(&unpadded, decryptedSig, len);
+        if (rc <= 0) {
+            ok = 0;
+        }
+        else {
+            XMEMCPY(decryptedSig, unpadded, rc);
+            rc--;
+        }
+    }
+    if (ok) {
+        if (unpadded[rc] != wp_rsa_get_x931_hash_code(
+    #if LIBWOLFSSL_VERSION_HEX >= 0x05007004
+            ctx->hash.type
+    #else
+            ctx->hashType
+    #endif
+        )) {
+            ok = 0;
+        }
+    }
+    if (ok && (((size_t)rc != tbsLen) || ((XMEMCMP(tbs, decryptedSig,
+            tbsLen) != 0)))) {
+        ok = 0;
+    }
+    if (NULL != unpadded) {
+        OPENSSL_free(unpadded);
+    }
+
+    WOLFPROV_LEAVE(WP_LOG_PK, __FILE__ ":" WOLFPROV_STRINGIZE(__LINE__), ok);
+    return ok;
+}
+
 /**
  * Verify an RSA signature.
  *
@@ -970,6 +1313,10 @@ static int wp_rsa_verify(wp_RsaSigCtx* ctx, const unsigned char* sig,
                 ok = wp_rsa_verify_no_pad(ctx, sig, sigLen, tbs, tbsLen,
                     decryptedSig);
             }
+            else if (ctx->padMode == RSA_X931_PADDING) {
+                ok = wp_rsa_verify_x931(ctx, sig, sigLen, tbs, tbsLen,
+                    decryptedSig);
+            }
             else {
                 ok = 0;
             }
@@ -1545,6 +1892,11 @@ static int wp_rsa_set_pad_mode(wp_RsaSigCtx* ctx, const OSSL_PARAM* p)
                 ok = 0;
             }
         }
+        else if (padMode == RSA_X931_PADDING) {
+            if (wp_rsa_get_type(ctx->rsa) != RSA_FLAG_TYPE_RSA) {
+                ok = 0;
+            }
+        }
         else {
             ok = 0;
         }
diff --git a/test/test_pkey.c b/test/test_pkey.c
index a71a0a04..ff03d140 100644
--- a/test/test_pkey.c
+++ b/test/test_pkey.c
@@ -96,15 +96,17 @@ int test_pkey_sign(EVP_PKEY *pkey, OSSL_LIB_CTX* libCtx, unsigned char *hash,
     if (err == 0) {
         err = EVP_PKEY_sign_init(ctx) != 1;
     }
+    /* Signature MD MUST be set before padding for ossl x931 */
+    if ((err == 0) && (padMode == RSA_PKCS1_PSS_PADDING ||
+            padMode == RSA_X931_PADDING) && rsaMd != NULL) {
+        err = EVP_PKEY_CTX_set_signature_md(ctx, rsaMd) <= 0;
+    }
     if ((err == 0) && padMode) {
         err = EVP_PKEY_CTX_set_rsa_padding(ctx, padMode) <= 0;
     }
     if ((err == 0) && padMode == RSA_PKCS1_PSS_PADDING) {
         err = EVP_PKEY_CTX_set_rsa_pss_saltlen(ctx, -1) < 0;
     }
-    if ((err == 0) && padMode == RSA_PKCS1_PSS_PADDING && rsaMd != NULL) {
-        err = EVP_PKEY_CTX_set_signature_md(ctx, rsaMd) <= 0;
-    }
     if ((err == 0) && padMode == RSA_PKCS1_PSS_PADDING && rsaMgf1Md != NULL) {
         err = EVP_PKEY_CTX_set_rsa_mgf1_md(ctx, rsaMgf1Md) <= 0;
     }
@@ -131,15 +133,17 @@ int test_pkey_verify(EVP_PKEY *pkey, OSSL_LIB_CTX* libCtx, unsigned char *hash,
     if (err == 0) {
         err = EVP_PKEY_verify_init(ctx) != 1;
     }
+    /* Signature MD MUST be set before padding for ossl x931 */
+    if ((err == 0) && (padMode == RSA_PKCS1_PSS_PADDING ||
+        padMode == RSA_X931_PADDING) && rsaMd != NULL) {
+        err = EVP_PKEY_CTX_set_signature_md(ctx, rsaMd) <= 0;
+    }
     if ((err == 0) && padMode) {
         err = EVP_PKEY_CTX_set_rsa_padding(ctx, padMode) <= 0;
     }
     if ((err == 0) && padMode == RSA_PKCS1_PSS_PADDING) {
         err = EVP_PKEY_CTX_set_rsa_pss_saltlen(ctx, -1) < 0;
     }
-    if ((err == 0) && padMode == RSA_PKCS1_PSS_PADDING && rsaMd != NULL) {
-        err = EVP_PKEY_CTX_set_signature_md(ctx, rsaMd) <= 0;
-    }
     if ((err == 0) && padMode == RSA_PKCS1_PSS_PADDING && rsaMgf1Md != NULL) {
         err = EVP_PKEY_CTX_set_rsa_mgf1_md(ctx, rsaMgf1Md) <= 0;
     }
diff --git a/test/test_rsa.c b/test/test_rsa.c
index 22b45677..74b1659a 100644
--- a/test/test_rsa.c
+++ b/test/test_rsa.c
@@ -269,6 +269,9 @@ static int test_rsa_sign_verify_pad(int padMode, const EVP_MD *md,
         if (padMode == RSA_NO_PADDING) {
             bufLen = rsaSigLen;
         }
+        else if (padMode == RSA_X931_PADDING) {
+            bufLen = EVP_MD_size(md);
+        }
         buf = (unsigned char *)OPENSSL_malloc(bufLen);
         err = buf == NULL;
     }
@@ -452,6 +455,40 @@ int test_rsa_sign_verify_pss(void *data)
     return err;
 }
 
+int test_rsa_sign_verify_x931(void *data)
+{
+
+    int err = 0;
+
+    (void)data;
+
+    /* Use SHA-1 (default) for MD and MGF1 MD. */
+    err = test_rsa_sign_verify_pad(RSA_X931_PADDING, EVP_sha1(), NULL) == 1;
+#ifdef WP_HAVE_SHA256
+    if (err == 0) {
+        /* Use SHA-256 for MD. */
+        err = test_rsa_sign_verify_pad(RSA_X931_PADDING, EVP_sha256(),
+                                       NULL) == 1;
+    }
+#endif
+#ifdef WP_HAVE_SHA384
+    if (err == 0) {
+        /* Use SHA-384 for MD. */
+        err = test_rsa_sign_verify_pad(RSA_X931_PADDING, EVP_sha384(),
+                                       NULL) == 1;
+    }
+#endif
+#ifdef WP_HAVE_SHA512
+    if (err == 0) {
+        /* Use SHA-512 for MD. */
+        err = test_rsa_sign_verify_pad(RSA_X931_PADDING, EVP_sha512(),
+                                       NULL) == 1;
+    }
+#endif
+
+    return err;
+}
+
 static int test_rsa_enc_dec(const unsigned char *der, size_t derLen,
                             int padMode, const EVP_MD *rsaMd,
                             const EVP_MD *rsaMgf1Md)
diff --git a/test/unit.c b/test/unit.c
index aadf77a3..344dd592 100644
--- a/test/unit.c
+++ b/test/unit.c
@@ -155,6 +155,7 @@ TEST_CASE test_case[] = {
     TEST_DECL(test_rsa_sign_sha1, NULL),
     TEST_DECL(test_rsa_sign_verify_pkcs1, NULL),
     TEST_DECL(test_rsa_sign_verify_pss, NULL),
+    TEST_DECL(test_rsa_sign_verify_x931, NULL),
     TEST_DECL(test_rsa_enc_dec_pkcs1, NULL),
     TEST_DECL(test_rsa_enc_dec_oaep, NULL),
     TEST_DECL(test_rsa_pkey_keygen, NULL),
diff --git a/test/unit.h b/test/unit.h
index 06ecaf0a..50ffc3d3 100644
--- a/test/unit.h
+++ b/test/unit.h
@@ -231,6 +231,7 @@ int test_pkey_dec_rsa(EVP_PKEY *pkey, unsigned char *msg, size_t msgLen,
 int test_rsa_sign_sha1(void *data);
 int test_rsa_sign_verify_pkcs1(void *data);
 int test_rsa_sign_verify_pss(void *data);
+int test_rsa_sign_verify_x931(void *data);
 int test_rsa_enc_dec_pkcs1(void *data);
 int test_rsa_enc_dec_oaep(void *data);
 int test_rsa_pkey_keygen(void *data);