EVP_ENCRYPTINIT(3)

NAME
EVP_CIPHER_CTX_new, EVP_CIPHER_CTX_reset, EVP_CIPHER_CTX_cleanup, EVP_CIPHER_CTX_init, EVP_CIPHER_CTX_free, EVP_CIPHER_CTX_copy, EVP_EncryptInit_ex, EVP_EncryptUpdate, EVP_EncryptFinal_ex, EVP_DecryptInit_ex, EVP_DecryptUpdate, EVP_DecryptFinal_ex, EVP_CipherInit_ex, EVP_CipherUpdate, EVP_CipherFinal_ex, EVP_EncryptInit, EVP_EncryptFinal, EVP_DecryptInit, EVP_DecryptFinal, EVP_CipherInit, EVP_CipherFinal, EVP_Cipher, EVP_CIPHER_CTX_encrypting, EVP_get_cipherbyname, EVP_get_cipherbynid, EVP_get_cipherbyobj, EVP_CIPHER_CTX_cipher, EVP_enc_null, EVP_idea_cbc, EVP_idea_ecb, EVP_idea_cfb64, EVP_idea_cfb, EVP_idea_ofb, EVP_rc2_cbc, EVP_rc2_ecb, EVP_rc2_cfb64, EVP_rc2_cfb, EVP_rc2_ofb, EVP_rc2_40_cbc, EVP_rc2_64_cbc, EVP_bf_cbc, EVP_bf_ecb, EVP_bf_cfb64, EVP_bf_cfb, EVP_bf_ofb, EVP_cast5_cbc, EVP_cast5_ecb, EVP_cast5_cfb64, EVP_cast5_cfb, EVP_cast5_ofb - EVP cipher routines

SYNOPSIS
#include <openssl/evp.h>
EVP_CIPHER_CTX *
EVP_CIPHER_CTX_new(void);
int
EVP_CIPHER_CTX_reset(EVP_CIPHER_CTX *ctx);
int
EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *ctx);
void
EVP_CIPHER_CTX_init(EVP_CIPHER_CTX *ctx);
void
EVP_CIPHER_CTX_free(EVP_CIPHER_CTX *ctx);
int
EVP_CIPHER_CTX_copy(EVP_CIPHER_CTX *out, const EVP_CIPHER_CTX *in);
int
EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, ENGINE *impl, const unsigned char *key, const unsigned char *iv);
int
EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl, const unsigned char *in, int inl);
int
EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
int
EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, ENGINE *impl, const unsigned char *key, const unsigned char *iv);
int
EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl, const unsigned char *in, int inl);
int
EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int
EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, ENGINE *impl, const unsigned char *key, const unsigned char *iv, int enc);
int
EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl, const unsigned char *in, int inl);
int
EVP_CipherFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int
EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, const unsigned char *key, const unsigned char *iv);
int
EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
int
EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, const unsigned char *key, const unsigned char *iv);
int
EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int
EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, const unsigned char *key, const unsigned char *iv, int enc);
int
EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl);
int
EVP_Cipher(EVP_CIPHER_CTX *ctx, unsigned char *out, const unsigned char *in, unsigned int inl);
int
EVP_CIPHER_CTX_encrypting(const EVP_CIPHER_CTX *ctx);
const EVP_CIPHER *
EVP_get_cipherbyname(const char *name);
const EVP_CIPHER *
EVP_get_cipherbynid(int nid);
const EVP_CIPHER *
EVP_get_cipherbyobj(const ASN1_OBJECT *a);
const EVP_CIPHER *
EVP_CIPHER_CTX_cipher(const EVP_CIPHER_CTX *ctx);

DESCRIPTION
The EVP cipher routines are a high level interface to certain symmetric ciphers.

EVP_CIPHER_CTX_new() creates a new, empty cipher context.

EVP_CIPHER_CTX_reset() clears all information from ctx and frees all allocated memory associated with it, except the ctx object itself, such that it can be reused for another series of calls to EVP_CipherInit(), EVP_CipherUpdate(), and EVP_CipherFinal(). EVP_CIPHER_CTX_cleanup() is a deprecated alias for EVP_CIPHER_CTX_reset().

EVP_CIPHER_CTX_init() is a deprecated function to clear a cipher context on the stack before use. Do not use it on a cipher context returned from EVP_CIPHER_CTX_new() or one that was already used.

EVP_CIPHER_CTX_free() clears all information from ctx and frees all allocated memory associated with it, including ctx itself. This function should be called after all operations using a cipher are complete, so sensitive information does not remain in memory. If ctx is a NULL pointer, no action occurs.

EVP_CIPHER_CTX_copy() calls EVP_CIPHER_CTX_reset() on out and copies all the data from in to out, except that the EVP_CIPHER and ENGINE objects used by in and any application specific data set with EVP_CIPHER_CTX_set_app_data(3) are not copied and out will point to the same three objects. The algorithm- and implementation-specific cipher data described in EVP_CIPHER_CTX_get_cipher_data(3) is copied with malloc(3) and memcpy(3), i.e. assuming that it does not contain pointers to any sub-objects. If the bit EVP_CIPH_CUSTOM_COPY has been set with EVP_CIPHER_meth_set_flags(3), EVP_CIPHER_CTX_ctrl(3) is called at the end with arguments in, EVP_CTRL_COPY, 0, and out such that the cipher implementation can perform further algorithm- and implementation-specific initializations after the algorithm- and implementation-specific cipher data has been copied. Among the cipher algorithms built into the library, EVP_CIPH_CUSTOM_COPY and EVP_CTRL_COPY are used by some of the ciphers documented in the EVP_aes_256_gcm(3) manual page.

EVP_EncryptInit_ex() sets up the cipher context ctx for encryption with cipher type from ENGINE impl. type is normally supplied by a function such as EVP_aes_256_cbc(3). If impl is NULL, then the default implementation is used. key is the symmetric key to use and iv is the IV to use (if necessary). The actual number of bytes used for the key and IV depends on the cipher. It is possible to set all parameters to NULL except type in an initial call and supply the remaining parameters in subsequent calls, all of which have type set to NULL. This is done when the default cipher parameters are not appropriate.

EVP_EncryptUpdate() encrypts inl bytes from the buffer in and writes the encrypted version to out. This function can be called multiple times to encrypt successive blocks of data. The amount of data written depends on the block alignment of the encrypted data: as a result the amount of data written may be anything from zero bytes to (inl + cipher_block_size - 1) so out should contain sufficient room. The actual number of bytes written is placed in outl.

If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts the "final" data, that is any data that remains in a partial block. It uses NOTES (aka PKCS padding). The encrypted final data is written to out which should have sufficient space for one cipher block. The number of bytes written is placed in outl. After this function is called, the encryption operation is finished and no further calls to EVP_EncryptUpdate() should be made.

If padding is disabled then EVP_EncryptFinal_ex() will not encrypt any more data and it will return an error if any data remains in a partial block: that is if the total data length is not a multiple of the block size.

EVP_DecryptInit_ex(), EVP_DecryptUpdate(), and EVP_DecryptFinal_ex() are the corresponding decryption operations. EVP_DecryptFinal() will return an error code if padding is enabled and the final block is not correctly formatted. The parameters and restrictions are identical to the encryption operations except that if padding is enabled the decrypted data buffer out passed to EVP_DecryptUpdate() should have sufficient room for (inl + cipher_block_size) bytes unless the cipher block size is 1 in which case inl bytes is sufficient.

EVP_CipherInit_ex(), EVP_CipherUpdate(), and EVP_CipherFinal_ex() are functions that can be used for decryption or encryption. The operation performed depends on the value of the enc parameter. It should be set to 1 for encryption, 0 for decryption and -1 to leave the value unchanged (the actual value of enc being supplied in a previous call).

EVP_EncryptInit(), EVP_DecryptInit(), and EVP_CipherInit() are deprecated functions behaving like EVP_EncryptInit_ex(), EVP_DecryptInit_ex(), and EVP_CipherInit_ex() except that they always use the default cipher implementation and that they require EVP_CIPHER_CTX_reset() before they can be used on a context that was already used.

EVP_EncryptFinal(), EVP_DecryptFinal(), and EVP_CipherFinal() are identical to EVP_EncryptFinal_ex(), EVP_DecryptFinal_ex(), and EVP_CipherFinal_ex(). In previous releases of OpenSSL, they also used to clean up the ctx, but this is no longer done and EVP_CIPHER_CTX_reset() or EVP_CIPHER_CTX_free() must be called to free any context resources.

EVP_Cipher() encrypts or decrypts aligned blocks of data whose lengths match the cipher block size. It requires that the previous encryption or decryption operation using the same ctx, if there was any, ended exactly on a block boundary and that inl is an integer multiple of the cipher block size. If either of these conditions is violated, EVP_Cipher() silently produces incorrect results. For that reason, using the function EVP_CipherUpdate() instead is strongly recommended. The latter can safely handle partial blocks, and even if inl actually is a multiple of the cipher block size for all calls, the overhead incurred by using EVP_CipherUpdate() is minimal.

EVP_get_cipherbyname(), EVP_get_cipherbynid(), and EVP_get_cipherbyobj() return an EVP_CIPHER structure when passed a cipher name, a NID or an ASN1_OBJECT structure.

EVP_CIPHER_CTX_cipher() returns the EVP_CIPHER structure when passed an EVP_CIPHER_CTX structure.

Where possible the EVP interface to symmetric ciphers should be used in preference to the low level interfaces. This is because the code then becomes transparent to the cipher used and much more flexible.

PKCS padding works by adding n padding bytes of value n to make the total length of the encrypted data a multiple of the block size. Padding is always added so if the data is already a multiple of the block size n will equal the block size. For example if the block size is 8 and 11 bytes are to be encrypted then 5 padding bytes of value 5 will be added.

When decrypting, the final block is checked to see if it has the correct form.

Although the decryption operation can produce an error if padding is enabled, it is not a strong test that the input data or key is correct. A random block has better than 1 in 256 chance of being of the correct format and problems with the input data earlier on will not produce a final decrypt error.

If padding is disabled then the decryption operation will always succeed if the total amount of data decrypted is a multiple of the block size.

The functions EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(), EVP_CipherInit(), and EVP_CipherFinal() are obsolete but are retained for compatibility with existing code. New code should use EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex(), and EVP_CipherFinal_ex() because they can reuse an existing context without allocating and freeing it up on each call.

EVP_get_cipherbynid() and EVP_get_cipherbyobj() are implemented as macros.

RETURN VALUES
EVP_CIPHER_CTX_new() returns a pointer to a newly created EVP_CIPHER_CTX for success or NULL for failure.

EVP_CIPHER_CTX_reset(), EVP_CIPHER_CTX_cleanup(), EVP_CIPHER_CTX_copy(), EVP_EncryptInit_ex(), EVP_EncryptUpdate(), EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptUpdate(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex(), EVP_CipherUpdate(), EVP_CipherFinal_ex(), EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(), EVP_DecryptFinal(), EVP_CipherInit(), EVP_CipherFinal(), and EVP_Cipher() return 1 for success or 0 for failure.

EVP_CIPHER_CTX_encrypting() returns 1 if ctx is initialized for encryption or 0 otherwise, in which case it may be uninitialized or initialized for decryption.

EVP_get_cipherbyname(), EVP_get_cipherbynid(), and EVP_get_cipherbyobj() return an EVP_CIPHER structure or NULL on error.

EVP_CIPHER_CTX_cipher() returns an EVP_CIPHER structure.

CIPHER LISTING
All algorithms have a fixed key length unless otherwise stated.

EVP_enc_null()
    Null cipher: does nothing.

    EVP_idea_cbc(), EVP_idea_ecb(), EVP_idea_cfb64(), EVP_idea_ofb() IDEA encryption algorithm in CBC, ECB, CFB and OFB modes respectively. EVP_idea_cfb() is an alias for EVP_idea_cfb64(), implemented as a macro.

    EVP_rc2_cbc(), EVP_rc2_ecb(), EVP_rc2_cfb64(), EVP_rc2_ofb() RC2 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length cipher with an additional parameter called "effective key bits" or "effective key length". By default both are set to 128 bits. EVP_rc2_cfb() is an alias for EVP_rc2_cfb64(), implemented as a macro.

    EVP_rc2_40_cbc(), EVP_rc2_64_cbc() RC2 algorithm in CBC mode with a default key length and effective key length of 40 and 64 bits. These are obsolete and new code should use EVP_rc2_cbc(), EVP_CIPHER_CTX_set_key_length(3), and EVP_CIPHER_CTX_ctrl(3) to set the key length and effective key length.

    EVP_bf_cbc(), EVP_bf_ecb(), EVP_bf_cfb64(), EVP_bf_ofb() Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length cipher. EVP_bf_cfb() is an alias for EVP_bf_cfb64(), implemented as a macro.

    EVP_cast5_cbc(), EVP_cast5_ecb(), EVP_cast5_cfb64(), EVP_cast5_ofb() CAST encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length cipher. EVP_cast5_cfb() is an alias for EVP_cast5_cfb64(), implemented as a macro.

See also EVP_aes_128_cbc(3), EVP_camellia_128_cbc(3), EVP_des_cbc(3), EVP_rc4(3), and EVP_sm4_cbc(3).

  GCM mode
For GCM mode ciphers, the behaviour of the EVP interface is subtly altered and several additional ctrl operations are supported.

To specify any additional authenticated data (AAD), a call to EVP_CipherUpdate(), EVP_EncryptUpdate(), or EVP_DecryptUpdate() should be made with the output parameter out set to NULL.

When decrypting, the return value of EVP_DecryptFinal() or EVP_CipherFinal() indicates if the operation was successful. If it does not indicate success, the authentication operation has failed and any output data MUST NOT be used as it is corrupted.

The following ctrls are supported in GCM mode:

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, ivlen, NULL)
    Sets the IV length: this call can only be made before specifying an IV. If not called, a default IV length is used. For GCM AES the default is 12, i.e. 96 bits.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, taglen, tag)
    Writes taglen bytes of the tag value to the buffer indicated by tag. This call can only be made when encrypting data and after all data has been processed, e.g. after an EVP_EncryptFinal() call.

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, taglen, tag)
    Sets the expected tag to taglen bytes from tag. This call is only legal when decrypting data and must be made before any data is processed, e.g. before any EVP_DecryptUpdate call.

  CCM mode
The behaviour of CCM mode ciphers is similar to GCM mode, but with a few additional requirements and different ctrl values.

Like GCM mode any additional authenticated data (AAD) is passed by calling EVP_CipherUpdate(), EVP_EncryptUpdate(), or EVP_DecryptUpdate() with the output parameter out set to NULL. Additionally, the total plaintext or ciphertext length MUST be passed to EVP_CipherUpdate(), EVP_EncryptUpdate(), or EVP_DecryptUpdate() with the output and input parameters (in and out) set to NULL and the length passed in the inl parameter.

The following ctrls are supported in CCM mode:

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, taglen, tag)
    This call is made to set the expected CCM tag value when decrypting or the length of the tag (with the tag parameter set to NULL) when encrypting. The tag length is often referred to as M. If not set, a default value is used (12 for AES).

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL)
    Sets the CCM L value. If not set, a default is used (8 for AES).

EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, ivlen, NULL)
    Sets the CCM nonce (IV) length: this call can only be made before specifying a nonce value. The nonce length is given by 15 - L so it is 7 by default for AES.

EXAMPLES
Encrypt a string using blowfish:

    int
    do_crypt(char *outfile)
    {
    	unsigned char outbuf[1024];
    	int outlen, tmplen;
    	/*
    	 * Bogus key and IV: we'd normally set these from
    	 * another source.
    	 */
    	unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
    	unsigned char iv[] = {1,2,3,4,5,6,7,8};
    	const char intext[] = "Some Crypto Text";
    	EVP_CIPHER_CTX *ctx;
    	FILE *out;
    	ctx = EVP_CIPHER_CTX_new();
    	EVP_EncryptInit_ex(ctx, EVP_bf_cbc(), NULL, key, iv);
    	if (!EVP_EncryptUpdate(ctx, outbuf, &outlen, intext,
    	    strlen(intext))) {
    		/* Error */
    		EVP_CIPHER_CTX_free(ctx);
    		return 0;
    	}
    	/*
    	 * Buffer passed to EVP_EncryptFinal() must be after data just
    	 * encrypted to avoid overwriting it.
    	 */
    	if (!EVP_EncryptFinal_ex(ctx, outbuf + outlen, &tmplen)) {
    		/* Error */
    		EVP_CIPHER_CTX_free(ctx);
    		return 0;
    	}
    	outlen += tmplen;
    	EVP_CIPHER_CTX_free(ctx);
    	/*
    	 * Need binary mode for fopen because encrypted data is
    	 * binary data. Also cannot use strlen() on it because
    	 * it won't be NUL terminated and may contain embedded
    	 * NULs.
    	 */
    	out = fopen(outfile, "wb");
    	if (out == NULL) {
    		/* Error */
    		return 0;
    	}
    	fwrite(outbuf, 1, outlen, out);
    	fclose(out);
    	return 1;
    }

The ciphertext from the above example can be decrypted using the openssl(1) utility with the command line:

    openssl bf -in cipher.bin -K 000102030405060708090A0B0C0D0E0F \
               -iv 0102030405060708 -d

General encryption, decryption function example using FILE I/O and AES128 with a 128-bit key:

    int
    do_crypt(FILE *in, FILE *out, int do_encrypt)
    {
    	/* Allow enough space in output buffer for additional block */
    	unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH];
    	int inlen, outlen;
    	EVP_CIPHER_CTX *ctx;
    	/*
    	 * Bogus key and IV: we'd normally set these from
    	 * another source.
    	 */
    	unsigned char key[] = "0123456789abcdeF";
    	unsigned char iv[] = "1234567887654321";
    	ctx = EVP_CIPHER_CTX_new();
    	EVP_CipherInit_ex(ctx, EVP_aes_128_cbc(), NULL, NULL, NULL,
    	    do_encrypt);
    	EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, do_encrypt);
    	for (;;) {
    		inlen = fread(inbuf, 1, 1024, in);
    		if (inlen <= 0)
    			break;
    		if (!EVP_CipherUpdate(ctx, outbuf, &outlen, inbuf,
    		    inlen)) {
    			/* Error */
    			EVP_CIPHER_CTX_free(ctx);
    			return 0;
    		}
    		fwrite(outbuf, 1, outlen, out);
    	}
    	if (!EVP_CipherFinal_ex(ctx, outbuf, &outlen)) {
    		/* Error */
    		EVP_CIPHER_CTX_free(ctx);
    		return 0;
    	}
    	fwrite(outbuf, 1, outlen, out);
    	EVP_CIPHER_CTX_free(ctx);
    	return 1;
    }

SEE ALSO
BIO_f_cipher(3), evp(3), EVP_AEAD_CTX_init(3), EVP_aes_128_cbc(3), EVP_camellia_128_cbc(3), EVP_chacha20(3), EVP_CIPHER_CTX_ctrl(3), EVP_CIPHER_CTX_get_cipher_data(3), EVP_CIPHER_CTX_set_flags(3), EVP_CIPHER_nid(3), EVP_des_cbc(3), EVP_OpenInit(3), EVP_rc4(3), EVP_SealInit(3), EVP_sm4_cbc(3)

HISTORY
EVP_EncryptInit(), EVP_EncryptUpdate(), EVP_EncryptFinal(), EVP_DecryptInit(), EVP_DecryptUpdate(), EVP_DecryptFinal(), EVP_CipherInit(), EVP_CipherUpdate(), EVP_CipherFinal(), EVP_get_cipherbyname(), EVP_idea_cbc(), EVP_idea_ecb(), EVP_idea_cfb(), and EVP_idea_ofb() first appeared in SSLeay 0.5.1. EVP_rc2_cbc(), EVP_rc2_ecb(), EVP_rc2_cfb(), and EVP_rc2_ofb() first appeared in SSLeay 0.5.2. EVP_Cipher() first appeared in SSLeay 0.6.5. EVP_bf_cbc(), EVP_bf_ecb(), EVP_bf_cfb(), and EVP_bf_ofb() first appeared in SSLeay 0.6.6. EVP_CIPHER_CTX_cleanup(), EVP_get_cipherbyobj(), EVP_CIPHER_CTX_cipher(), and EVP_enc_null() first appeared in SSLeay 0.8.0. EVP_get_cipherbynid() first appeared in SSLeay 0.8.1. EVP_CIPHER_CTX_init() first appeared in SSLeay 0.9.0. All these functions have been available since OpenBSD 2.4.

EVP_rc2_40_cbc() and EVP_rc2_64_cbc() first appeared in SSLeay 0.9.1 and have been available since OpenBSD 2.6.

EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex(), and EVP_CipherFinal_ex() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.

EVP_bf_cfb64(), EVP_cast5_cfb64(), EVP_idea_cfb64(), and EVP_rc2_cfb64() first appeared in OpenSSL 0.9.7e and have been available since OpenBSD 3.8.

EVP_CIPHER_CTX_new() and EVP_CIPHER_CTX_free() first appeared in OpenSSL 0.9.8b and have been available since OpenBSD 4.5.

EVP_CIPHER_CTX_copy() first appeared in OpenSSL 1.0.0 and has been available since OpenBSD 4.9.

EVP_CIPHER_CTX_reset() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.3.

EVP_CIPHER_CTX_encrypting() first appeared in OpenSSL 1.1.0 and has been available since OpenBSD 6.4.

BUGS
EVP_CIPHER_CTX_copy() may already have cleared the data in out and copied some new data into it even if it fails and returns 0.