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(Lianja) Encrypting a Data StreamThis example illustrates encrypting a large dataset using symmetric encryption algorithms like
You can provide data chunks smaller than the encryption algorithm's block size. For example, AES uses 16-byte blocks;
Chilkat handles the buffering of data as needed. If a data chunk smaller than the block size is provided, an empty string (or 0 bytes) is returned, and the data is buffered to be combined with subsequent chunks. The final chunk is padded to the algorithm's block size (as determined by the Chunk-wise decryption follows the same procedure as chunk-wise encryption.
// This example requires the Chilkat API to have been previously unlocked. // See Global Unlock Sample for sample code. loCrypt = createobject("CkCrypt2") loCrypt.CryptAlgorithm = "aes" loCrypt.CipherMode = "cbc" loCrypt.KeyLength = 128 loCrypt.SetEncodedKey("000102030405060708090A0B0C0D0E0F","hex") loCrypt.SetEncodedIV("000102030405060708090A0B0C0D0E0F","hex") loCrypt.EncodingMode = "hex" lcTxt1 = "The quick brown fox jumped over the lazy dog." + Chr(13) + Chr(10) lcTxt2 = "-" + Chr(13) + Chr(10) lcTxt3 = "Done." + Chr(13) + Chr(10) loSbEncrypted = createobject("CkStringBuilder") // Encrypt the 1st chunk: // (don't worry about feeding the data to the encryptor in // exact multiples of the encryption algorithm's block size. // Chilkat will buffer the data.) loCrypt.FirstChunk = .T. loCrypt.LastChunk = .F. loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt1)) // Encrypt the 2nd chunk loCrypt.FirstChunk = .F. loCrypt.LastChunk = .F. loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt2)) // Now encrypt N more chunks... // Remember -- we're doing this in CBC mode, so each call // to the encrypt method depends on the state from previous // calls... loCrypt.FirstChunk = .F. loCrypt.LastChunk = .F. for i = 0 to 4 loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt1)) loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt2)) next // Now encrypt the last chunk: loCrypt.FirstChunk = .F. loCrypt.LastChunk = .T. loSbEncrypted.Append(loCrypt.EncryptStringENC(lcTxt3)) ? loSbEncrypted.GetAsString() // Now decrypt in one call. // (The data we're decrypting is both the first AND last chunk.) loCrypt.FirstChunk = .T. loCrypt.LastChunk = .T. lcDecryptedText = loCrypt.DecryptStringENC(loSbEncrypted.GetAsString()) ? lcDecryptedText // Note: You may decrypt in N chunks by setting the FirstChunk // and LastChunk properties prior to calling the Decrypt* methods release loCrypt release loSbEncrypted |
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