ASN1_STRING_PRINT_EX(3) | Library Functions Manual | ASN1_STRING_PRINT_EX(3)

# NAME

`ASN1_STRING_print_ex`, `ASN1_STRING_print_ex_fp`, `ASN1_STRING_print`, `ASN1_tag2str` — ASN1_STRING output routines

# SYNOPSIS

library “libcrypto”
`#include <openssl/asn1.h>`

int
`ASN1_STRING_print_ex`(BIO *out, const ASN1_STRING *str, unsigned long flags);

int
`ASN1_STRING_print_ex_fp`(FILE *fp, const ASN1_STRING *str, unsigned long flags);

int
`ASN1_STRING_print`(BIO *out, const ASN1_STRING *str);

const char *
`ASN1_tag2str`(int tag);

# DESCRIPTION

These functions output an ASN1_STRING structure. ASN1_STRING is used to represent all the ASN.1 string types.

`ASN1_STRING_print_ex`() outputs str to out, the format being determined by the options flags. `ASN1_STRING_print_ex_fp`() is identical except it outputs to fp instead.

`ASN1_STRING_print`() prints str to out but using a different format to `ASN1_STRING_print_ex`(). It replaces unprintable characters (other than CR, LF) with ‘.’.

`ASN1_tag2str`() returns a human-readable name of the specified ASN.1 tag.

`ASN1_STRING_print`() is a deprecated function which should be avoided; use `ASN1_STRING_print_ex`() instead.

Although there are a large number of options, `ASN1_STRFLGS_RFC2253` is often suitable, or on UTF-8 terminals `ASN1_STRFLGS_RFC2253` and ~`ASN1_STRFLGS_ESC_MSB`.

The complete set of supported options for flags is listed below.

Various characters can be escaped. If `ASN1_STRFLGS_ESC_2253` is set, the characters determined by RFC 2253 are escaped. If `ASN1_STRFLGS_ESC_CTRL` is set, control characters are escaped. If `ASN1_STRFLGS_ESC_MSB` is set, characters with the MSB set are escaped: this option should not be used if the terminal correctly interprets UTF-8 sequences.

Escaping takes several forms. If the character being escaped is a 16-bit character then the form "\UXXXX" is used using exactly four characters for the hex representation. If it is 32 bits then "\WXXXXXXXX" is used using eight characters of its hex representation. These forms will only be used if UTF-8 conversion is not set (see below).

Printable characters are normally escaped using the backslash (‘\’) character. If `ASN1_STRFLGS_ESC_QUOTE` is set, then the whole string is instead surrounded by double quote characters: this is arguably more readable than the backslash notation. Other characters use the "\XX" using exactly two characters of the hex representation.

If `ASN1_STRFLGS_UTF8_CONVERT` is set, then characters are converted to UTF-8 format first. If the terminal supports the display of UTF-8 sequences then this option will correctly display multi-byte characters.

If `ASN1_STRFLGS_IGNORE_TYPE` is set, then the string type is not interpreted at all: everything is assumed to be one byte per character. This is primarily for debugging purposes and can result in confusing output in multi-character strings.

If `ASN1_STRFLGS_SHOW_TYPE` is set, then the string type itself is printed before its value (for example "BMPSTRING"), using `ASN1_tag2str`().

Instead of being interpreted the contents of a string can be "dumped": this just outputs the value of the string using the form #XXXX using hex format for each octet.

If `ASN1_STRFLGS_DUMP_ALL` is set, then any type is dumped.

Normally non-character string types (such as OCTET STRING) are assumed to be one byte per character; if `ASN1_STRFLGS_DUMP_UNKNOWN` is set, then they will be dumped instead.

When a type is dumped normally just the content octets are printed; if `ASN1_STRFLGS_DUMP_DER` is set, then the complete encoding is dumped instead (including tag and length octets).

`ASN1_STRFLGS_RFC2253` includes all the flags required by RFC 2253. It is equivalent to `ASN1_STRFLGS_ESC_2253` | `ASN1_STRFLGS_ESC_CTRL` | `ASN1_STRFLGS_ESC_MSB` | `ASN1_STRFLGS_UTF8_CONVERT` | `ASN1_STRFLGS_DUMP_UNKNOWN` | `ASN1_STRFLGS_DUMP_DER`.

# RETURN VALUES

`ASN1_STRING_print_ex`() and `ASN1_STRING_print_ex_fp`() return the number of characters written or -1 if an error occurred.

`ASN1_STRING_print`() returns 1 on success or 0 on error.

`ASN1_tag2str`() returns a static string.

# SEE ALSO

ASN1_parse_dump(3), ASN1_STRING_new(3), X509_NAME_print_ex(3), X509_signature_dump(3)

# HISTORY

`ASN1_STRING_print`() first appeared in SSLeay 0.6.5 and has been available since OpenBSD 2.4.

`ASN1_tag2str`() first appeared in OpenSSL 0.9.5 and has been available since OpenBSD 2.7.

`ASN1_STRING_print_ex`() and `ASN1_STRING_print_ex_fp`() first appeared in OpenSSL 0.9.6 and have been available since OpenBSD 2.9.

June 8, 2025 | Debian