diff --git a/src/iperf.h b/src/iperf.h
index c1d839be1..527e549ed 100644
--- a/src/iperf.h
+++ b/src/iperf.h
@@ -319,6 +319,7 @@ struct iperf_test
     char      *server_authorized_users;
     EVP_PKEY  *server_rsa_private_key;
     int       server_skew_threshold;
+    int       use_pkcs1_padding;
 #endif // HAVE_SSL
 
     /* boolean variables for Options */
diff --git a/src/iperf3.1 b/src/iperf3.1
index 2efd53dea..2561414f5 100644
--- a/src/iperf3.1
+++ b/src/iperf3.1
@@ -193,6 +193,15 @@ parameter is specified in ms, and defaults to the system settings.
 This functionality depends on the TCP_USER_TIMEOUT socket option, and
 will not work on systems that do not support it.
 .TP
+.BR --use-pkcs1-padding
+This option is only meaningful when using iperf3's authentication
+features. Versions of iperf3 prior to 3.17 used PCKS1 padding in the
+RSA-encrypted credentials, which was vulnerable to a side-channel
+attack that could reveal a server's private key.  Beginning with
+iperf-3.17, OAEP padding is used, however this is a breaking change
+that is not compatible with older iperf3 versions.  Use this option to
+preserve the less secure, but more compatible, behavior.
+.TP
 .BR -d ", " --debug " "
 emit debugging output.
 Primarily (perhaps exclusively) of use to developers.
diff --git a/src/iperf_api.c b/src/iperf_api.c
index d40561c10..7fb741e77 100644
--- a/src/iperf_api.c
+++ b/src/iperf_api.c
@@ -1137,6 +1137,7 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
     {"rsa-private-key-path", required_argument, NULL, OPT_SERVER_RSA_PRIVATE_KEY},
     {"authorized-users-path", required_argument, NULL, OPT_SERVER_AUTHORIZED_USERS},
     {"time-skew-threshold", required_argument, NULL, OPT_SERVER_SKEW_THRESHOLD},
+    {"use-pkcs1-padding", no_argument, NULL, OPT_USE_PKCS1_PADDING},
 #endif /* HAVE_SSL */
 	{"fq-rate", required_argument, NULL, OPT_FQ_RATE},
 	{"pacing-timer", required_argument, NULL, OPT_PACING_TIMER},
@@ -1630,6 +1631,9 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
                 return -1;
             }
             break;
+	case OPT_USE_PKCS1_PADDING:
+	    test->use_pkcs1_padding = 1;
+	    break;
 #endif /* HAVE_SSL */
 	    case OPT_PACING_TIMER:
 		test->settings->pacing_timer = unit_atoi(optarg);
@@ -2070,7 +2074,7 @@ int test_is_authorized(struct iperf_test *test){
     if (test->settings->authtoken){
         char *username = NULL, *password = NULL;
         time_t ts;
-        int rc = decode_auth_setting(test->debug, test->settings->authtoken, test->server_rsa_private_key, &username, &password, &ts);
+        int rc = decode_auth_setting(test->debug, test->settings->authtoken, test->server_rsa_private_key, &username, &password, &ts, test->use_pkcs1_padding);
 	if (rc) {
 	    return -1;
 	}
@@ -2255,7 +2259,7 @@ send_parameters(struct iperf_test *test)
 #if defined(HAVE_SSL)
 	/* Send authentication parameters */
 	if (test->settings->client_username && test->settings->client_password && test->settings->client_rsa_pubkey){
-	    int rc = encode_auth_setting(test->settings->client_username, test->settings->client_password, test->settings->client_rsa_pubkey, &test->settings->authtoken);
+	    int rc = encode_auth_setting(test->settings->client_username, test->settings->client_password, test->settings->client_rsa_pubkey, &test->settings->authtoken, test->use_pkcs1_padding);
 
 	    if (rc) {
 		cJSON_Delete(j);
diff --git a/src/iperf_api.h b/src/iperf_api.h
index d2bbdfe96..131314243 100644
--- a/src/iperf_api.h
+++ b/src/iperf_api.h
@@ -100,6 +100,7 @@ typedef atomic_uint_fast64_t atomic_iperf_size_t;
 #define OPT_RCV_TIMEOUT 27
 #define OPT_JSON_STREAM 28
 #define OPT_SND_TIMEOUT 29
+#define OPT_USE_PKCS1_PADDING 30
 
 /* states */
 #define TEST_START 1
diff --git a/src/iperf_auth.c b/src/iperf_auth.c
index c89bde7c3..72e85fc9a 100644
--- a/src/iperf_auth.c
+++ b/src/iperf_auth.c
@@ -230,7 +230,7 @@ int test_load_private_key_from_file(const char *file){
     return 0;
 }
 
-int encrypt_rsa_message(const char *plaintext, EVP_PKEY *public_key, unsigned char **encryptedtext) {
+int encrypt_rsa_message(const char *plaintext, EVP_PKEY *public_key, unsigned char **encryptedtext, int use_pkcs1_padding) {
 #if OPENSSL_VERSION_MAJOR >= 3
     EVP_PKEY_CTX *ctx;
 #else
@@ -257,12 +257,19 @@ int encrypt_rsa_message(const char *plaintext, EVP_PKEY *public_key, unsigned ch
 
     BIO *bioBuff   = BIO_new_mem_buf((void*)plaintext, (int)strlen(plaintext));
     rsa_buffer_len = BIO_read(bioBuff, rsa_buffer, keysize * 2);
+
+    int padding = RSA_PKCS1_OAEP_PADDING;
+    if (use_pkcs1_padding){
+        padding = RSA_PKCS1_PADDING;
+    }
 #if OPENSSL_VERSION_MAJOR >= 3
     EVP_PKEY_encrypt_init(ctx);
+    EVP_PKEY_CTX_set_rsa_padding(ctx, padding);
+
     EVP_PKEY_encrypt(ctx, *encryptedtext, &encryptedtext_len, rsa_buffer, rsa_buffer_len);
     EVP_PKEY_CTX_free(ctx);
 #else
-    encryptedtext_len = RSA_public_encrypt(rsa_buffer_len, rsa_buffer, *encryptedtext, rsa, RSA_PKCS1_PADDING);
+    encryptedtext_len = RSA_public_encrypt(rsa_buffer_len, rsa_buffer, *encryptedtext, rsa, padding);
     RSA_free(rsa);
 #endif
 
@@ -280,7 +287,7 @@ int encrypt_rsa_message(const char *plaintext, EVP_PKEY *public_key, unsigned ch
     return 0;
 }
 
-int decrypt_rsa_message(const unsigned char *encryptedtext, const int encryptedtext_len, EVP_PKEY *private_key, unsigned char **plaintext) {
+int decrypt_rsa_message(const unsigned char *encryptedtext, const int encryptedtext_len, EVP_PKEY *private_key, unsigned char **plaintext, int use_pkcs1_padding) {
 #if OPENSSL_VERSION_MAJOR >= 3
     EVP_PKEY_CTX *ctx;
 #else
@@ -307,21 +314,31 @@ int decrypt_rsa_message(const unsigned char *encryptedtext, const int encryptedt
 
     BIO *bioBuff   = BIO_new_mem_buf((void*)encryptedtext, encryptedtext_len);
     rsa_buffer_len = BIO_read(bioBuff, rsa_buffer, keysize * 2);
+
+    int padding = RSA_PKCS1_OAEP_PADDING;
+    if (use_pkcs1_padding){
+        padding = RSA_PKCS1_PADDING;
+    }
 #if OPENSSL_VERSION_MAJOR >= 3
     plaintext_len = keysize;
     EVP_PKEY_decrypt_init(ctx);
+    int ret = EVP_PKEY_CTX_set_rsa_padding(ctx, padding);
+    if (ret < 0){
+        goto errreturn;
+    }
     EVP_PKEY_decrypt(ctx, *plaintext, &plaintext_len, rsa_buffer, rsa_buffer_len);
     EVP_PKEY_CTX_free(ctx);
 #else
-    plaintext_len = RSA_private_decrypt(rsa_buffer_len, rsa_buffer, *plaintext, rsa, RSA_PKCS1_PADDING);
+    plaintext_len = RSA_private_decrypt(rsa_buffer_len, rsa_buffer, *plaintext, rsa, padding);
     RSA_free(rsa);
 #endif
 
     OPENSSL_free(rsa_buffer);
     BIO_free(bioBuff);
 
-    if (plaintext_len <= 0) {
-        goto errreturn;
+    /* Treat a decryption error as an empty string. */
+    if (plaintext_len < 0) {
+        plaintext_len = 0;
     }
 
     return plaintext_len;
@@ -331,7 +348,7 @@ int decrypt_rsa_message(const unsigned char *encryptedtext, const int encryptedt
     return 0;
 }
 
-int encode_auth_setting(const char *username, const char *password, EVP_PKEY *public_key, char **authtoken){
+int encode_auth_setting(const char *username, const char *password, EVP_PKEY *public_key, char **authtoken, int use_pkcs1_padding){
     time_t t = time(NULL);
     time_t utc_seconds = mktime(localtime(&t));
 
@@ -348,7 +365,7 @@ int encode_auth_setting(const char *username, const char *password, EVP_PKEY *pu
 
     unsigned char *encrypted = NULL;
     int encrypted_len;
-    encrypted_len = encrypt_rsa_message(text, public_key, &encrypted);
+    encrypted_len = encrypt_rsa_message(text, public_key, &encrypted, use_pkcs1_padding);
     free(text);
     if (encrypted_len < 0) {
       return -1;
@@ -359,7 +376,7 @@ int encode_auth_setting(const char *username, const char *password, EVP_PKEY *pu
     return (0); //success
 }
 
-int decode_auth_setting(int enable_debug, const char *authtoken, EVP_PKEY *private_key, char **username, char **password, time_t *ts){
+int decode_auth_setting(int enable_debug, const char *authtoken, EVP_PKEY *private_key, char **username, char **password, time_t *ts, int use_pkcs1_padding){
     unsigned char *encrypted_b64 = NULL;
     size_t encrypted_len_b64;
     int64_t utc_seconds;
@@ -367,7 +384,7 @@ int decode_auth_setting(int enable_debug, const char *authtoken, EVP_PKEY *priva
 
     unsigned char *plaintext = NULL;
     int plaintext_len;
-    plaintext_len = decrypt_rsa_message(encrypted_b64, encrypted_len_b64, private_key, &plaintext);
+    plaintext_len = decrypt_rsa_message(encrypted_b64, encrypted_len_b64, private_key, &plaintext, use_pkcs1_padding);
     free(encrypted_b64);
     if (plaintext_len < 0) {
         return -1;
diff --git a/src/iperf_auth.h b/src/iperf_auth.h
index ffadbf3e5..eedd45abd 100644
--- a/src/iperf_auth.h
+++ b/src/iperf_auth.h
@@ -35,7 +35,7 @@ EVP_PKEY *load_pubkey_from_file(const char *file);
 EVP_PKEY *load_pubkey_from_base64(const char *buffer);
 EVP_PKEY *load_privkey_from_file(const char *file);
 EVP_PKEY *load_privkey_from_base64(const char *buffer);
-int encode_auth_setting(const char *username, const char *password, EVP_PKEY *public_key, char **authtoken);
-int decode_auth_setting(int enable_debug, const char *authtoken, EVP_PKEY *private_key, char **username, char **password, time_t *ts);
+int encode_auth_setting(const char *username, const char *password, EVP_PKEY *public_key, char **authtoken, int use_pkcs1_padding);
+int decode_auth_setting(int enable_debug, const char *authtoken, EVP_PKEY *private_key, char **username, char **password, time_t *ts, int use_pkcs1_padding);
 int check_authentication(const char *username, const char *password, const time_t ts, const char *filename, int skew_threshold);
 ssize_t iperf_getpass (char **lineptr, size_t *n, FILE *stream);
diff --git a/src/iperf_locale.c b/src/iperf_locale.c
index ae0f63a41..9d94e0234 100644
--- a/src/iperf_locale.c
+++ b/src/iperf_locale.c
@@ -148,6 +148,7 @@ const char usage_longstr[] = "Usage: iperf3 [-s|-c host] [options]\n"
                            "                            credentials\n"
                            "  --time-skew-threshold     time skew threshold (in seconds) between the server\n"
                            "                            and client during the authentication process\n"
+                           "  --use-pkcs1-padding       use pkcs1 padding at your own risk\n"
 #endif //HAVE_SSL
                            "Client specific:\n"
                            "  -c, --client <host>[%%<dev>] run in client mode, connecting to <host>\n"
diff --git a/src/t_auth.c b/src/t_auth.c
index 77c225531..3b0fd2f32 100644
--- a/src/t_auth.c
+++ b/src/t_auth.c
@@ -101,8 +101,9 @@ test_authtoken(const char *authUser, const char *authPassword, EVP_PKEY *pubkey,
     char *decodePassword;
     time_t decodeTime;
 
-    assert(encode_auth_setting(authUser, authPassword, pubkey, &authToken) == 0);
-    assert(decode_auth_setting(0, authToken, privkey, &decodeUser, &decodePassword, &decodeTime) == 0);
+    int use_pkcs1_padding = 1;
+    assert(encode_auth_setting(authUser, authPassword, pubkey, &authToken, use_pkcs1_padding) == 0);
+    assert(decode_auth_setting(0, authToken, privkey, &decodeUser, &decodePassword, &decodeTime, use_pkcs1_padding) == 0);
 
     assert(strcmp(decodeUser, authUser) == 0);
     assert(strcmp(decodePassword, authPassword) == 0);