X509V3_EXT_PRINT(3) | Library Functions Manual | X509V3_EXT_PRINT(3)

# NAME

`X509V3_EXT_print`, `X509V3_EXT_print_fp` — pretty-print an X.509 extension

# SYNOPSIS

library “libcrypto”
`#include <openssl/x509v3.h>`

int
`X509V3_EXT_print`(BIO *bio, X509_EXTENSION *ext, unsigned long flags, int indent);

int
`X509V3_EXT_print_fp`(FILE *file, X509_EXTENSION *ext, int flags, int indent);

# DESCRIPTION

`X509V3_EXT_print`() and `X509V3_EXT_print_fp`() decode ext and print the data contained in it to the bio or file, respectively, in a human-readable format with a left margin of indent space characters. The details of both the decoding and the printing depend on the type of ext.

For most extension types, the decoding is done in the same way as it would be done by the appropriate public API function, for example:

extension type
  decoding function
`NID_authority_key_identifier`
  d2i_AUTHORITY_KEYID(3)
`NID_certificate_policies`
  d2i_CERTIFICATEPOLICIES(3)
`NID_crl_number`
  d2i_ASN1_INTEGER(3)
`NID_crl_reason`
  d2i_ASN1_ENUMERATED(3)
`NID_hold_instruction_code`
  d2i_ASN1_OBJECT(3)
`NID_id_pkix_OCSP_CrlID`
  d2i_OCSP_CRLID(3)
`NID_id_pkix_OCSP_noCheck`
  d2i_ASN1_NULL(3)
`NID_id_pkix_OCSP_Nonce`
  non-public function built into the library
`NID_invalidity_date`
  d2i_ASN1_GENERALIZEDTIME(3)
`NID_key_usage`
  d2i_ASN1_BIT_STRING(3)
`NID_subject_alt_name`
  d2i_GENERAL_NAMES(3)
`NID_subject_key_identifier`
  d2i_ASN1_OCTET_STRING(3)

For some types, the printing is performed by a dedicated non-public function built into the library. For some other types, the printing function is a public API function, for example:

extension type
  printing function
`NID_crl_number`
  i2s_ASN1_INTEGER(3)
`NID_crl_reason`
  i2s_ASN1_ENUMERATED_TABLE(3)
`NID_delta_crl`
  i2s_ASN1_INTEGER(3)
`NID_hold_instruction_code`
  i2a_ASN1_OBJECT(3)
`NID_id_pkix_OCSP_archiveCutoff`
  ASN1_GENERALIZEDTIME_print(3)
`NID_id_pkix_OCSP_Nonce`
  i2a_ASN1_STRING(3)
`NID_inhibit_any_policy`
  i2s_ASN1_INTEGER(3)
`NID_invalidity_date`
  ASN1_GENERALIZEDTIME_print(3)
`NID_key_usage`
  i2v_ASN1_BIT_STRING(3)
`NID_subject_key_identifier`
  i2s_ASN1_OCTET_STRING(3)

Some of the public printing functions are not documented yet.

If ext is of an unknown extension type or if decoding fails while using the decoding function for the relevant type, the action taken depends on the flags argument:

- If the bit `X509V3_EXT_PARSE_UNKNOWN` is set, ASN1_parse_dump(3) is called on the BER-encoded data of the extension, passing -1 for the dump argument. Thus, some information about the encoding of the extension gets printed and some about its decoded content, falling back to BIO_dump_indent(3) for the decoded content unless a dedicated printing method is known for the respective data type(s). Note that even if an extension type is unknown, the data type used by the unknown extension, or, if that data type is constructed, of the values contained in it, may still be known, which may allow printing the content of even an unknown extension in a structured or partially structured form.
- If the bit `X509V3_EXT_DUMP_UNKNOWN` is set, BIO_dump_indent(3) is called on the BER-encoded data of the extension without decoding it first, which is usually less readable than the above but poses a smaller risk of omitting or misrepresenting parts of the information.
- If the bit `X509V3_EXT_ERROR_UNKNOWN` is set, only the fixed string "<Not Supported>" is printed for an unknown type or only the fixed string "<Parse Error>" if the parsing functions fails, but printing is considered as successful anyway.
- If more than one of these three bits is set, or if a bit in `X509V3_EXT_UNKNOWN_MASK` is set that is not listed above, nothing is printed, but printing is considered as successful anyway.
- If none of the bits in `X509V3_EXT_UNKNOWN_MASK` are set, nothing is printed and printing is considered as failed.

# RETURN VALUES

`X509V3_EXT_print`() and `X509V3_EXT_print_fp`() return 0 if failure was both detected and considered relevant. Otherwise, 1 is returned, and in general the user cannot tell whether failure simply went undetected, whether the function detected failure but regarded it as irrelevant, or whether printing did indeed succeed.

# SEE ALSO

BIO_new(3), X509_EXTENSION_new(3), X509_get0_extensions(3), X509_get_ext(3), X509V3_extensions_print(3)

# HISTORY

These functions first appeared in OpenSSL 0.9.2 and have been available since OpenBSD 2.6.

# BUGS

These functions lack error handling throughout. When a write operation fails, they will usually ignore the fact that information was omitted from the output and report success to the caller anyway.

June 8, 2025 | Debian