ASN1_STRING_PRINT_EX(3ossl)

🌸 NAME 🌸

ASN1_tag2str, ASN1_STRING_print_ex, ASN1_STRING_print_ex_fp, ASN1_STRING_print — bestie, these are the ASN1_STRING output routines 💅

(also hey, this page lives in section 3ossl of the OpenSSL manual, that's the ASN1_STRING_PRINT_EX(3ossl) situation, ok let's go ✨)

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🎀 SYNOPSIS 🎀

#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);

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💖 DESCRIPTION 💖

okay so these functions output an ASN1_STRING structure. and like, ASN1_STRING is the thing that represents all the ASN1 string types, it's the main character of string representation fr fr 👑

ASN1_STRING_print_ex() outputs str to out, and the format is determined by the options in flags. ASN1_STRING_print_ex_fp() is literally the identical twin except it outputs to fp instead. same energy, different destination 🫶

ASN1_STRING_print() prints str to out but with a different format than ASN1_STRING_print_ex(). the way it works: it replaces unprintable characters (other than CR, LF) with . — that's it, that's the whole vibe.

ASN1_tag2str() returns a human-readable name of the specified ASN.1 tag. iconic behavior tbh ✨

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📝 NOTES 📝

⚠️ ASN1_STRING_print() is a deprecated function which should be avoided; use ASN1_STRING_print_ex() instead. no cap, don't use the old one bestie 😭

Although there are a large number of options, frequently ASN1_STRFLGS_RFC2253 is suitable, or on UTF8 terminals ASN1_STRFLGS_RFC2253 & ~ASN1_STRFLGS_ESC_MSB. (yes the ~ is doing its thing, we love a bitwise moment 💅)

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

Various characters can be escaped:

• ASN1_STRFLGS_ESC_2253 — if set, the characters determined by RFC2253 are escaped.
• ASN1_STRFLGS_ESC_CTRL — if set, control characters are escaped.
• ASN1_STRFLGS_ESC_MSB — if set, characters with the MSB set are escaped. this option should not be used if the terminal correctly interprets UTF8 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 UTF8 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" form, using exactly two characters of the hex representation.

If ASN1_STRFLGS_UTF8_CONVERT is set then characters are converted to UTF8 format first. If the terminal supports the display of UTF8 sequences then this option will correctly display multi byte characters. slay 🌈

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. like, it's giving chaos, you've been warned 💀

If ASN1_STRFLGS_SHOW_TYPE is set then the string type itself is printed out before its value (for example "BMPSTRING"), this actually uses ASN1_tag2str(). cute callback 🎀

The content of a string, instead of being interpreted, 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 RFC2253. 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

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🔥 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 human-readable name of the specified ASN.1 tag.

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🦋 SEE ALSO 🦋

• X509_NAME_print_ex(3)
• ASN1_tag2str(3)

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👑 COPYRIGHT 👑

Copyright 2002-2018 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>.

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ok that's the whole page bestie, you ate 💅✨ this was 3.5.9, dated 2026-09-29, straight from OpenSSL — now go print some strings, you've got this 🫶💖🌸