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opensslaespadding
aspirino67
aspirino67

Reputation: 405

OpenSSL EVP_CIPHER_CTX_set_padding not working

I am trying to encrypt/decrypt using AES, CBC and PKCS#7 padding using the EVP interface. I am using the example found on the Wiki.

I am doing EVP_CIPHER_CTX_set_padding(ctx, 0) after creating and initializing the context which should not add padding and fail if the plaintext is not a multiple of 16 bytes. Despite this the ciphertext always contains an extra block made up of padding only.

The code I am using is literally copied and pasted from the tutorial, I am only adding EVP_CIPHER_CTX_set_padding(ctx, 0) in both encrypt and decrypt like so:

/* Create and initialise the context */
if (!(ctx = EVP_CIPHER_CTX_new())) handleErrors();
EVP_CIPHER_CTX_set_padding(ctx, 0);

Am I doing something wrong?

Upvotes: 3

Views: 5341

Answers (1)

aspirino67
aspirino67

Reputation: 405

Apparently both EVP_DecryptInit_ex and EVP_EncryptInit_ex re-initialize the context so any context changes (such as setting the padding) should be performed after those methods have been called.

Upvotes: 8

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