diff --git a/crypto/err/err_prn.c b/crypto/err/err_prn.c
index 5c4ebcbddd..80cc0ecf1a 100644
--- a/crypto/err/err_prn.c
+++ b/crypto/err/err_prn.c
@@ -35,8 +35,9 @@ void ERR_print_errors_cb(int (*cb) (const char *str, size_t len, void *u),
             func = "unknown function";
         if ((flags & ERR_TXT_STRING) == 0)
             data = "";
-        hex = OPENSSL_buf2hexstr((const unsigned char *)&tid, sizeof(tid));
-        BIO_snprintf(buf, sizeof(buf), "%s:error:%s:%s:%s:%s:%d:%s\n",
+        hex = openssl_buf2hexstr_sep((const unsigned char *)&tid, sizeof(tid),
+                                     '\0');
+        BIO_snprintf(buf, sizeof(buf), "%s:error::%s:%s:%s:%s:%d:%s\n",
                      hex == NULL ? "<null>" : hex, lib, func, reason, file,
                      line, data);
         OPENSSL_free(hex);
diff --git a/crypto/o_str.c b/crypto/o_str.c
index 6780188cda..6578857b94 100644
--- a/crypto/o_str.c
+++ b/crypto/o_str.c
@@ -12,6 +12,9 @@
 #include <openssl/crypto.h>
 #include "internal/cryptlib.h"
 
+#define DEFAULT_SEPARATOR ':'
+#define CH_ZERO '\0'
+
 char *CRYPTO_strdup(const char *str, const char* file, int line)
 {
     char *ret;
@@ -37,7 +40,7 @@ char *CRYPTO_strndup(const char *str, size_t s, const char* file, int line)
     ret = CRYPTO_malloc(maxlen + 1, file, line);
     if (ret) {
         memcpy(ret, str, maxlen);
-        ret[maxlen] = '\0';
+        ret[maxlen] = CH_ZERO;
     }
     return ret;
 }
@@ -61,7 +64,7 @@ size_t OPENSSL_strnlen(const char *str, size_t maxlen)
 {
     const char *p;
 
-    for (p = str; maxlen-- != 0 && *p != '\0'; ++p) ;
+    for (p = str; maxlen-- != 0 && *p != CH_ZERO; ++p) ;
 
     return p - str;
 }
@@ -74,7 +77,7 @@ size_t OPENSSL_strlcpy(char *dst, const char *src, size_t size)
         l++;
     }
     if (size)
-        *dst = '\0';
+        *dst = CH_ZERO;
     return l + strlen(src);
 }
 
@@ -129,11 +132,8 @@ int OPENSSL_hexchar2int(unsigned char c)
     return -1;
 }
 
-/*
- * Give a string of hex digits convert to a buffer
- */
-int OPENSSL_hexstr2buf_ex(unsigned char *buf, size_t buf_n, size_t *buflen,
-                          const char *str)
+static int hexstr2buf_sep(unsigned char *buf, size_t buf_n, size_t *buflen,
+                          const char *str, const char sep)
 {
     unsigned char *q;
     unsigned char ch, cl;
@@ -143,26 +143,24 @@ int OPENSSL_hexstr2buf_ex(unsigned char *buf, size_t buf_n, size_t *buflen,
 
     for (p = (const unsigned char *)str, q = buf, cnt = 0; *p; ) {
         ch = *p++;
-        if (ch == ':')
+        /* A separator of CH_ZERO means there is no separator */
+        if (ch == sep && sep != CH_ZERO)
             continue;
         cl = *p++;
         if (!cl) {
-            CRYPTOerr(CRYPTO_F_OPENSSL_HEXSTR2BUF_EX,
-                      CRYPTO_R_ODD_NUMBER_OF_DIGITS);
+            CRYPTOerr(0, CRYPTO_R_ODD_NUMBER_OF_DIGITS);
             return 0;
         }
         cli = OPENSSL_hexchar2int(cl);
         chi = OPENSSL_hexchar2int(ch);
         if (cli < 0 || chi < 0) {
-            CRYPTOerr(CRYPTO_F_OPENSSL_HEXSTR2BUF_EX,
-                      CRYPTO_R_ILLEGAL_HEX_DIGIT);
+            CRYPTOerr(0, CRYPTO_R_ILLEGAL_HEX_DIGIT);
             return 0;
         }
         cnt++;
         if (q != NULL) {
             if (cnt > buf_n) {
-                CRYPTOerr(CRYPTO_F_OPENSSL_HEXSTR2BUF_EX,
-                          CRYPTO_R_TOO_SMALL_BUFFER);
+                CRYPTOerr(0, CRYPTO_R_TOO_SMALL_BUFFER);
                 return 0;
             }
             *q++ = (unsigned char)((chi << 4) | cli);
@@ -174,21 +172,31 @@ int OPENSSL_hexstr2buf_ex(unsigned char *buf, size_t buf_n, size_t *buflen,
     return 1;
 }
 
-unsigned char *OPENSSL_hexstr2buf(const char *str, long *buflen)
+/*
+ * Given a string of hex digits convert to a buffer
+ */
+int OPENSSL_hexstr2buf_ex(unsigned char *buf, size_t buf_n, size_t *buflen,
+                          const char *str)
+{
+    return hexstr2buf_sep(buf, buf_n, buflen, str, DEFAULT_SEPARATOR);
+}
+
+unsigned char *openssl_hexstr2buf_sep(const char *str, long *buflen,
+                                      const char sep)
 {
     unsigned char *buf;
     size_t buf_n, tmp_buflen;
 
     buf_n = strlen(str) >> 1;
     if ((buf = OPENSSL_malloc(buf_n)) == NULL) {
-        CRYPTOerr(CRYPTO_F_OPENSSL_HEXSTR2BUF, ERR_R_MALLOC_FAILURE);
+        CRYPTOerr(0, ERR_R_MALLOC_FAILURE);
         return NULL;
     }
 
     if (buflen != NULL)
         *buflen = 0;
     tmp_buflen = 0;
-    if (OPENSSL_hexstr2buf_ex(buf, buf_n, &tmp_buflen, str)) {
+    if (hexstr2buf_sep(buf, buf_n, &tmp_buflen, str, sep)) {
         if (buflen != NULL)
             *buflen = (long)tmp_buflen;
         return buf;
@@ -197,21 +205,29 @@ unsigned char *OPENSSL_hexstr2buf(const char *str, long *buflen)
     return NULL;
 }
 
-int OPENSSL_buf2hexstr_ex(char *str, size_t str_n, size_t *strlen,
-                          const unsigned char *buf, size_t buflen)
+unsigned char *OPENSSL_hexstr2buf(const char *str, long *buflen)
+{
+    return openssl_hexstr2buf_sep(str, buflen, DEFAULT_SEPARATOR);
+}
+
+static int buf2hexstr_sep(char *str, size_t str_n, size_t *strlen,
+                          const unsigned char *buf, size_t buflen,
+                          const char sep)
 {
     static const char hexdig[] = "0123456789ABCDEF";
     const unsigned char *p;
     char *q;
     size_t i;
+    int has_sep = (sep != CH_ZERO);
+    size_t len = has_sep ? buflen * 3 : 1 + buflen * 2;
 
     if (strlen != NULL)
-        *strlen = buflen * 3;
+        *strlen = len;
     if (str == NULL)
         return 1;
 
-    if (str_n < (unsigned long)buflen * 3) {
-        CRYPTOerr(CRYPTO_F_OPENSSL_BUF2HEXSTR_EX, CRYPTO_R_TOO_SMALL_BUFFER);
+    if (str_n < (unsigned long)len) {
+        CRYPTOerr(0, CRYPTO_R_TOO_SMALL_BUFFER);
         return 0;
     }
 
@@ -219,15 +235,46 @@ int OPENSSL_buf2hexstr_ex(char *str, size_t str_n, size_t *strlen,
     for (i = 0, p = buf; i < buflen; i++, p++) {
         *q++ = hexdig[(*p >> 4) & 0xf];
         *q++ = hexdig[*p & 0xf];
-        *q++ = ':';
+        if (has_sep)
+            *q++ = sep;
     }
-    q[-1] = 0;
+    if (has_sep)
+        --q;
+    *q = CH_ZERO;
+
 #ifdef CHARSET_EBCDIC
     ebcdic2ascii(str, str, q - str - 1);
 #endif
     return 1;
 }
 
+int OPENSSL_buf2hexstr_ex(char *str, size_t str_n, size_t *strlen,
+                          const unsigned char *buf, size_t buflen)
+{
+    return buf2hexstr_sep(str, str_n, strlen, buf, buflen, DEFAULT_SEPARATOR);
+}
+
+char *openssl_buf2hexstr_sep(const unsigned char *buf, long buflen, char sep)
+{
+    char *tmp;
+    size_t tmp_n;
+
+    if (buflen == 0)
+        return OPENSSL_zalloc(1);
+
+    tmp_n = (sep != CH_ZERO) ? buflen * 3 : 1 + buflen * 2;
+    if ((tmp = OPENSSL_malloc(tmp_n)) == NULL) {
+        CRYPTOerr(0, ERR_R_MALLOC_FAILURE);
+        return NULL;
+    }
+
+    if (buf2hexstr_sep(tmp, tmp_n, NULL, buf, buflen, sep))
+        return tmp;
+    OPENSSL_free(tmp);
+    return NULL;
+}
+
+
 /*
  * Given a buffer of length 'len' return a OPENSSL_malloc'ed string with its
  * hex representation @@@ (Contents of buffer are always kept in ASCII, also
@@ -235,22 +282,7 @@ int OPENSSL_buf2hexstr_ex(char *str, size_t str_n, size_t *strlen,
  */
 char *OPENSSL_buf2hexstr(const unsigned char *buf, long buflen)
 {
-    char *tmp;
-    size_t tmp_n;
-
-    if (buflen == 0)
-        return OPENSSL_zalloc(1);
-
-    tmp_n = buflen * 3;
-    if ((tmp = OPENSSL_malloc(tmp_n)) == NULL) {
-        CRYPTOerr(CRYPTO_F_OPENSSL_BUF2HEXSTR, ERR_R_MALLOC_FAILURE);
-        return NULL;
-    }
-
-    if (OPENSSL_buf2hexstr_ex(tmp, tmp_n, NULL, buf, buflen))
-        return tmp;
-    OPENSSL_free(tmp);
-    return NULL;
+    return openssl_buf2hexstr_sep(buf, buflen, ':');
 }
 
 int openssl_strerror_r(int errnum, char *buf, size_t buflen)
diff --git a/include/internal/cryptlib.h b/include/internal/cryptlib.h
index b479b58a84..a4f18a5d3f 100644
--- a/include/internal/cryptlib.h
+++ b/include/internal/cryptlib.h
@@ -241,4 +241,8 @@ char *sk_ASN1_UTF8STRING2text(STACK_OF(ASN1_UTF8STRING) *text, const char *sep,
                               size_t max_len);
 char *ipaddr_to_asc(unsigned char *p, int len);
 
+char *openssl_buf2hexstr_sep(const unsigned char *buf, long buflen, char sep);
+unsigned char *openssl_hexstr2buf_sep(const char *str, long *buflen,
+                                      const char sep);
+
 #endif
diff --git a/test/build.info b/test/build.info
index 112b68c22f..9697e55f12 100644
--- a/test/build.info
+++ b/test/build.info
@@ -54,7 +54,7 @@ IF[{- !$disabled{tests} -}]
           http_test servername_test ocspapitest fatalerrtest tls13ccstest \
           sysdefaulttest errtest ssl_ctx_test gosttest \
           context_internal_test aesgcmtest params_test evp_pkey_dparams_test \
-          keymgmt_internal_test
+          keymgmt_internal_test hexstr_test
 
   SOURCE[confdump]=confdump.c
   INCLUDE[confdump]=../include ../apps/include
@@ -736,6 +736,11 @@ IF[{- !$disabled{tests} -}]
   INCLUDE[params_test]=.. ../include ../apps/include
   DEPEND[params_test]=../libcrypto.a libtestutil.a
 
+  PROGRAMS{noinst}=hexstr_test
+  SOURCE[hexstr_test]=hexstr_test.c
+  INCLUDE[hexstr_test]=.. ../include ../apps/include
+  DEPEND[hexstr_test]=../libcrypto.a libtestutil.a
+
   PROGRAMS{noinst}=namemap_internal_test
   SOURCE[namemap_internal_test]=namemap_internal_test.c
   INCLUDE[namemap_internal_test]=.. ../include ../apps/include
diff --git a/test/errtest.c b/test/errtest.c
index 179c338c45..cc2f6612d1 100644
--- a/test/errtest.c
+++ b/test/errtest.c
@@ -7,6 +7,7 @@
  * https://www.openssl.org/source/license.html
  */
 
+#include <string.h>
 #include <openssl/opensslconf.h>
 #include <openssl/err.h>
 
@@ -18,6 +19,46 @@
 # include <errno.h>
 #endif
 
+#ifndef OPENSSL_NO_DEPRECATED_3_0
+# define IS_HEX(ch) ((ch >= '0' && ch <='9') || (ch >= 'A' && ch <='F'))
+
+static int test_print_error_format(void)
+{
+    static const char expected[] =
+        ":error::system library:test_print_error_format:Operation not permitted:"
+# ifndef OPENSSL_NO_FILENAMES
+        "errtest.c:30:";
+# else
+        ":0:";
+# endif
+    char *out = NULL, *p = NULL;
+    int ret = 0, len;
+    BIO *bio = NULL;
+
+    if (!TEST_ptr(bio = BIO_new(BIO_s_mem())))
+        return 0;
+
+    ERR_PUT_error(ERR_LIB_SYS, 0, 1, "errtest.c", 30);
+    ERR_print_errors(bio);
+
+    if (!TEST_int_gt(len = BIO_get_mem_data(bio, &out), 0))
+        goto err;
+    /* Skip over the variable thread id at the start of the string */
+    for (p = out; *p != ':' && *p != 0; ++p) {
+        if (!TEST_true(IS_HEX(*p)))
+            goto err;
+    }
+    if (!TEST_true(*p != 0)
+        || !TEST_strn_eq(expected, p, strlen(expected)))
+        goto err;
+
+    ret = 1;
+err:
+    BIO_free(bio);
+    return ret;
+}
+#endif
+
 /* Test that querying the error queue preserves the OS error. */
 static int preserves_system_error(void)
 {
@@ -79,5 +120,8 @@ int setup_tests(void)
     ADD_TEST(preserves_system_error);
     ADD_TEST(vdata_appends);
     ADD_TEST(raised_error);
+#ifndef OPENSSL_NO_DEPRECATED_3_0
+    ADD_TEST(test_print_error_format);
+#endif
     return 1;
 }
diff --git a/test/hexstr_test.c b/test/hexstr_test.c
new file mode 100644
index 0000000000..c4f13b6d53
--- /dev/null
+++ b/test/hexstr_test.c
@@ -0,0 +1,133 @@
+/*
+ * Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * https://www.openssl.org/source/license.html
+ * or in the file LICENSE in the source distribution.
+ */
+
+/*
+ * This program tests the use of OSSL_PARAM, currently in raw form.
+ */
+
+#include "internal/nelem.h"
+#include "internal/cryptlib.h"
+#include "testutil.h"
+
+struct testdata
+{
+    const char *in;
+    const unsigned char *expected;
+    size_t expected_len;
+    const char sep;
+};
+
+static const unsigned char test_1[] = { 0xAB, 0xCD, 0xEF, 0xF1 };
+static const unsigned char test_2[] = { 0xAB, 0xCD, 0xEF, 0x76, 0x00 };
+
+static struct testdata tbl_testdata[] = {
+    {
+        "AB:CD:EF:F1",
+        test_1, sizeof(test_1),
+        ':',
+    },
+    {
+        "AB:CD:EF:76:00",
+        test_2, sizeof(test_2),
+        ':',
+    },
+    {
+        "AB_CD_EF_F1",
+        test_1, sizeof(test_1),
+        '_',
+    },
+    {
+        "AB_CD_EF_76_00",
+        test_2, sizeof(test_2),
+        '_',
+    },
+    {
+        "ABCDEFF1",
+        test_1, sizeof(test_1),
+        '\0',
+    },
+    {
+        "ABCDEF7600",
+        test_2, sizeof(test_2),
+        '\0',
+    },
+};
+
+static int test_hexstr_sep_to_from(int test_index)
+{
+    int ret = 0;
+    long len = 0;
+    unsigned char *buf = NULL;
+    char *out = NULL;
+    struct testdata *test = &tbl_testdata[test_index];
+
+    if (!TEST_ptr(buf = openssl_hexstr2buf_sep(test->in, &len, test->sep))
+        || !TEST_mem_eq(buf, len, test->expected, test->expected_len)
+        || !TEST_ptr(out = openssl_buf2hexstr_sep(buf, len, test->sep))
+        || !TEST_str_eq(out, test->in))
+       goto err;
+
+    ret = 1;
+err:
+    OPENSSL_free(buf);
+    OPENSSL_free(out);
+    return ret;
+}
+
+static int test_hexstr_to_from(int test_index)
+{
+    int ret = 0;
+    long len = 0;
+    unsigned char *buf = NULL;
+    char *out = NULL;
+    struct testdata *test = &tbl_testdata[test_index];
+
+    if (test->sep != '_') {
+        if (!TEST_ptr(buf = OPENSSL_hexstr2buf(test->in, &len))
+            || !TEST_mem_eq(buf, len, test->expected, test->expected_len)
+            || !TEST_ptr(out = OPENSSL_buf2hexstr(buf, len)))
+           goto err;
+        if (test->sep == ':') {
+            if (!TEST_str_eq(out, test->in))
+                goto err;
+        } else if (!TEST_str_ne(out, test->in)) {
+            goto err;
+        }
+    } else {
+        if (!TEST_ptr_null(buf = OPENSSL_hexstr2buf(test->in, &len)))
+            goto err;
+    }
+    ret = 1;
+err:
+    OPENSSL_free(buf);
+    OPENSSL_free(out);
+    return ret;
+}
+
+static int test_hexstr_ex_to_from(int test_index)
+{
+    size_t len = 0;
+    char out[64];
+    unsigned char buf[64];
+    struct testdata *test = &tbl_testdata[test_index];
+
+    return TEST_true(OPENSSL_hexstr2buf_ex(buf, sizeof(buf), &len, test->in))
+           && TEST_mem_eq(buf, len, test->expected, test->expected_len)
+           && TEST_true(OPENSSL_buf2hexstr_ex(out, sizeof(out), NULL, buf, len))
+           && TEST_str_eq(out, test->in);
+}
+
+int setup_tests(void)
+{
+    ADD_ALL_TESTS(test_hexstr_sep_to_from, OSSL_NELEM(tbl_testdata));
+    ADD_ALL_TESTS(test_hexstr_to_from, OSSL_NELEM(tbl_testdata));
+    ADD_ALL_TESTS(test_hexstr_ex_to_from, 2);
+    return 1;
+}
diff --git a/test/recipes/04-test_hexstring.t b/test/recipes/04-test_hexstring.t
new file mode 100644
index 0000000000..664868fe60
--- /dev/null
+++ b/test/recipes/04-test_hexstring.t
@@ -0,0 +1,15 @@
+#! /usr/bin/env perl
+# Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the Apache License 2.0 (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
+
+use strict;
+use OpenSSL::Test;
+use OpenSSL::Test::Simple;
+
+setup("test_hexstring");
+
+simple_test("test_hexstring", "hexstr_test");