EVP_EncodeInit.pod 6.6 KB

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  1. =pod
  2. =head1 NAME
  3. EVP_EncodeInit, EVP_EncodeUpdate, EVP_EncodeFinal, EVP_EncodeBlock,
  4. EVP_DecodeInit, EVP_DecodeUpdate, EVP_DecodeFinal, EVP_DecodeBlock - EVP base 64
  5. encode/decode routines
  6. =head1 SYNOPSIS
  7. #include <openssl/evp.h>
  8. void EVP_EncodeInit(EVP_ENCODE_CTX *ctx);
  9. void EVP_EncodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
  10. const unsigned char *in, int inl);
  11. void EVP_EncodeFinal(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl);
  12. int EVP_EncodeBlock(unsigned char *t, const unsigned char *f, int n);
  13. void EVP_DecodeInit(EVP_ENCODE_CTX *ctx);
  14. int EVP_DecodeUpdate(EVP_ENCODE_CTX *ctx, unsigned char *out, int *outl,
  15. const unsigned char *in, int inl);
  16. int EVP_DecodeFinal(EVP_ENCODE_CTX *ctx, unsigned
  17. char *out, int *outl);
  18. int EVP_DecodeBlock(unsigned char *t, const unsigned char *f, int n);
  19. =head1 DESCRIPTION
  20. The EVP encode routines provide a high level interface to base 64 encoding and
  21. decoding. Base 64 encoding converts binary data into a printable form that uses
  22. the characters A-Z, a-z, 0-9, "+" and "/" to represent the data. For every 3
  23. bytes of binary data provided 4 bytes of base 64 encoded data will be produced
  24. plus some occasional newlines (see below). If the input data length is not a
  25. multiple of 3 then the output data will be padded at the end using the "="
  26. character.
  27. Encoding of binary data is performed in blocks of 48 input bytes (or less for
  28. the final block). For each 48 byte input block encoded 64 bytes of base 64 data
  29. is output plus an additional newline character (i.e. 65 bytes in total). The
  30. final block (which may be less than 48 bytes) will output 4 bytes for every 3
  31. bytes of input. If the data length is not divisible by 3 then a full 4 bytes is
  32. still output for the final 1 or 2 bytes of input. Similarly a newline character
  33. will also be output.
  34. EVP_EncodeInit() initialises B<ctx> for the start of a new encoding operation.
  35. EVP_EncodeUpdate() encode B<inl> bytes of data found in the buffer pointed to by
  36. B<in>. The output is stored in the buffer B<out> and the number of bytes output
  37. is stored in B<*outl>. It is the caller's responsibility to ensure that the
  38. buffer at B<out> is sufficiently large to accommodate the output data. Only full
  39. blocks of data (48 bytes) will be immediately processed and output by this
  40. function. Any remainder is held in the B<ctx> object and will be processed by a
  41. subsequent call to EVP_EncodeUpdate() or EVP_EncodeFinal(). To calculate the
  42. required size of the output buffer add together the value of B<inl> with the
  43. amount of unprocessed data held in B<ctx> and divide the result by 48 (ignore
  44. any remainder). This gives the number of blocks of data that will be processed.
  45. Ensure the output buffer contains 65 bytes of storage for each block, plus an
  46. additional byte for a NUL terminator. EVP_EncodeUpdate() may be called
  47. repeatedly to process large amounts of input data. In the event of an error
  48. EVP_EncodeUpdate() will set B<*outl> to 0.
  49. EVP_EncodeFinal() must be called at the end of an encoding operation. It will
  50. process any partial block of data remaining in the B<ctx> object. The output
  51. data will be stored in B<out> and the length of the data written will be stored
  52. in B<*outl>. It is the caller's responsibility to ensure that B<out> is
  53. sufficiently large to accommodate the output data which will never be more than
  54. 65 bytes plus an additional NUL terminator (i.e. 66 bytes in total).
  55. EVP_EncodeBlock() encodes a full block of input data in B<f> and of length
  56. B<dlen> and stores it in B<t>. For every 3 bytes of input provided 4 bytes of
  57. output data will be produced. If B<dlen> is not divisible by 3 then the block is
  58. encoded as a final block of data and the output is padded such that it is always
  59. divisible by 4. Additionally a NUL terminator character will be added. For
  60. example if 16 bytes of input data is provided then 24 bytes of encoded data is
  61. created plus 1 byte for a NUL terminator (i.e. 25 bytes in total). The length of
  62. the data generated I<without> the NUL terminator is returned from the function.
  63. EVP_DecodeInit() initialises B<ctx> for the start of a new decoding operation.
  64. EVP_DecodeUpdate() decodes B<inl> characters of data found in the buffer pointed
  65. to by B<in>. The output is stored in the buffer B<out> and the number of bytes
  66. output is stored in B<*outl>. It is the caller's responsibility to ensure that
  67. the buffer at B<out> is sufficiently large to accommodate the output data. This
  68. function will attempt to decode as much data as possible in 4 byte chunks. Any
  69. whitespace, newline or carriage return characters are ignored. Any partial chunk
  70. of unprocessed data (1, 2 or 3 bytes) that remains at the end will be held in
  71. the B<ctx> object and processed by a subsequent call to EVP_DecodeUpdate(). If
  72. any illegal base 64 characters are encountered or if the base 64 padding
  73. character "=" is encountered in the middle of the data then the function returns
  74. -1 to indicate an error. A return value of 0 or 1 indicates successful
  75. processing of the data. A return value of 0 additionally indicates that the last
  76. input data characters processed included the base 64 padding character "=" and
  77. therefore no more non-padding character data is expected to be processed. For
  78. every 4 valid base 64 bytes processed (ignoring whitespace, carriage returns and
  79. line feeds), 3 bytes of binary output data will be produced (or less at the end
  80. of the data where the padding character "=" has been used).
  81. EVP_DecodeFinal() must be called at the end of a decoding operation. If there
  82. is any unprocessed data still in B<ctx> then the input data must not have been
  83. a multiple of 4 and therefore an error has occurred. The function will return -1
  84. in this case. Otherwise the function returns 1 on success.
  85. EVP_DecodeBlock() will decode the block of B<n> characters of base 64 data
  86. contained in B<f> and store the result in B<t>. Any leading whitespace will be
  87. trimmed as will any trailing whitespace, newlines, carriage returns or EOF
  88. characters. After such trimming the length of the data in B<f> must be divisbile
  89. by 4. For every 4 input bytes exactly 3 output bytes will be produced. The
  90. output will be padded with 0 bits if necessary to ensure that the output is
  91. always 3 bytes for every 4 input bytes. This function will return the length of
  92. the data decoded or -1 on error.
  93. =head1 RETURN VALUES
  94. EVP_EncodeBlock() returns the number of bytes encoded excluding the NUL
  95. terminator.
  96. EVP_DecodeUpdate() returns -1 on error and 0 or 1 on success. If 0 is returned
  97. then no more non-padding base 64 characters are expected.
  98. EVP_DecodeFinal() returns -1 on error or 1 on success.
  99. EVP_DecodeBlock() returns the length of the data decoded or -1 on error.
  100. =head1 SEE ALSO
  101. L<evp(3)>
  102. =cut