RAND_bytes.pod 3.7 KB

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  1. =pod
  2. =head1 NAME
  3. RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex,
  4. RAND_pseudo_bytes - generate random data
  5. =head1 SYNOPSIS
  6. #include <openssl/rand.h>
  7. int RAND_bytes(unsigned char *buf, int num);
  8. int RAND_priv_bytes(unsigned char *buf, int num);
  9. int RAND_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
  10. unsigned int strength);
  11. int RAND_priv_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
  12. unsigned int strength);
  13. The following function has been deprecated since OpenSSL 1.1.0, and can be
  14. hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
  15. see L<openssl_user_macros(7)>:
  16. int RAND_pseudo_bytes(unsigned char *buf, int num);
  17. =head1 DESCRIPTION
  18. RAND_bytes() generates B<num> random bytes using a cryptographically
  19. secure pseudo random generator (CSPRNG) and stores them in B<buf>.
  20. RAND_priv_bytes() has the same semantics as RAND_bytes(). It is intended to
  21. be used for generating values that should remain private. If using the
  22. default RAND_METHOD, this function uses a separate "private" PRNG
  23. instance so that a compromise of the "public" PRNG instance will not
  24. affect the secrecy of these private values, as described in L<RAND(7)>
  25. and L<EVP_RAND(7)>.
  26. RAND_bytes_ex() and RAND_priv_bytes_ex() are the same as RAND_bytes() and
  27. RAND_priv_bytes() except that they both take additional I<strength> and
  28. I<ctx> parameters. The bytes generated will have a security strength of at
  29. least I<strength> bits.
  30. The DRBG used for the operation is the public or private DRBG associated with
  31. the specified I<ctx>. The parameter can be NULL, in which case
  32. the default library context is used (see L<OSSL_LIB_CTX(3)>.
  33. If the default RAND_METHOD has been changed then for compatibility reasons the
  34. RAND_METHOD will be used in preference and the DRBG of the library context
  35. ignored.
  36. =head1 NOTES
  37. By default, the OpenSSL CSPRNG supports a security level of 256 bits, provided it
  38. was able to seed itself from a trusted entropy source.
  39. On all major platforms supported by OpenSSL (including the Unix-like platforms
  40. and Windows), OpenSSL is configured to automatically seed the CSPRNG on first use
  41. using the operating systems's random generator.
  42. If the entropy source fails or is not available, the CSPRNG will enter an
  43. error state and refuse to generate random bytes. For that reason, it is important
  44. to always check the error return value of RAND_bytes() and RAND_priv_bytes() and
  45. not take randomness for granted.
  46. On other platforms, there might not be a trusted entropy source available
  47. or OpenSSL might have been explicitly configured to use different entropy sources.
  48. If you are in doubt about the quality of the entropy source, don't hesitate to ask
  49. your operating system vendor or post a question on GitHub or the openssl-users
  50. mailing list.
  51. =head1 RETURN VALUES
  52. RAND_bytes() and RAND_priv_bytes()
  53. return 1 on success, -1 if not supported by the current
  54. RAND method, or 0 on other failure. The error code can be
  55. obtained by L<ERR_get_error(3)>.
  56. =head1 SEE ALSO
  57. L<RAND_add(3)>,
  58. L<RAND_bytes(3)>,
  59. L<RAND_priv_bytes(3)>,
  60. L<ERR_get_error(3)>,
  61. L<RAND(7)>,
  62. L<EVP_RAND(7)>
  63. =head1 HISTORY
  64. =over 2
  65. =item *
  66. RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead.
  67. =item *
  68. The RAND_priv_bytes() function was added in OpenSSL 1.1.1.
  69. =item *
  70. The RAND_bytes_ex() and RAND_priv_bytes_ex() functions were added in OpenSSL 3.0
  71. =back
  72. =head1 COPYRIGHT
  73. Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
  74. Licensed under the Apache License 2.0 (the "License"). You may not use
  75. this file except in compliance with the License. You can obtain a copy
  76. in the file LICENSE in the source distribution or at
  77. L<https://www.openssl.org/source/license.html>.
  78. =cut