Class: OpenSSL::Cipher

Inherits:
Object
  • Object
show all
Defined in:
ossl_cipher.c,
lib/openssl/cipher.rb,
ossl_cipher.c

Overview

Provides symmetric algorithms for encryption and decryption. The algorithms that are available depend on the particular version of OpenSSL that is installed.

Listing all supported algorithms

A list of supported algorithms can be obtained by

puts OpenSSL::Cipher.ciphers

Instantiating a Cipher

There are several ways to create a Cipher instance. Generally, a Cipher algorithm is categorized by its name, the key length in bits and the cipher mode to be used. The most generic way to create a Cipher is the following

cipher = OpenSSL::Cipher.new('<name>-<key length>-<mode>')

That is, a string consisting of the hyphenated concatenation of the individual components name, key length and mode. Either all uppercase or all lowercase strings may be used, for example:

cipher = OpenSSL::Cipher.new('AES-128-CBC')

For each algorithm supported, there is a class defined under the Cipher class that goes by the name of the cipher, e.g. to obtain an instance of AES, you could also use

# these are equivalent
cipher = OpenSSL::Cipher::AES.new(128, :CBC)
cipher = OpenSSL::Cipher::AES.new(128, 'CBC')
cipher = OpenSSL::Cipher::AES.new('128-CBC')

Finally, due to its wide-spread use, there are also extra classes defined for the different key sizes of AES

cipher = OpenSSL::Cipher::AES128.new(:CBC)
cipher = OpenSSL::Cipher::AES192.new(:CBC)
cipher = OpenSSL::Cipher::AES256.new(:CBC)

Choosing either encryption or decryption mode

Encryption and decryption are often very similar operations for symmetric algorithms, this is reflected by not having to choose different classes for either operation, both can be done using the same class. Still, after obtaining a Cipher instance, we need to tell the instance what it is that we intend to do with it, so we need to call either

cipher.encrypt

or

cipher.decrypt

on the Cipher instance. This should be the first call after creating the instance, otherwise configuration that has already been set could get lost in the process.

Choosing a key

Symmetric encryption requires a key that is the same for the encrypting and for the decrypting party and after initial key establishment should be kept as private information. There are a lot of ways to create insecure keys, the most notable is to simply take a password as the key without processing the password further. A simple and secure way to create a key for a particular Cipher is

cipher = OpenSSL::AES256.new(:CFB)
cipher.encrypt
key = cipher.random_key # also sets the generated key on the Cipher

If you absolutely need to use passwords as encryption keys, you should use Password-Based Key Derivation Function 2 (PBKDF2) by generating the key with the help of the functionality provided by OpenSSL::PKCS5.pbkdf2_hmac_sha1 or OpenSSL::PKCS5.pbkdf2_hmac.

Although there is Cipher#pkcs5_keyivgen, its use is deprecated and it should only be used in legacy applications because it does not use the newer PKCS#5 v2 algorithms.

Choosing an IV

The cipher modes CBC, CFB, OFB and CTR all need an “initialization vector”, or short, IV. ECB mode is the only mode that does not require an IV, but there is almost no legitimate use case for this mode because of the fact that it does not sufficiently hide plaintext patterns. Therefore

You should never use ECB mode unless you are absolutely sure that you absolutely need it

Because of this, you will end up with a mode that explicitly requires an IV in any case. Note that for backwards compatibility reasons, setting an IV is not explicitly mandated by the Cipher API. If not set, OpenSSL itself defaults to an all-zeroes IV (“\0”, not the character). Although the IV can be seen as public information, i.e. it may be transmitted in public once generated, it should still stay unpredictable to prevent certain kinds of attacks. Therefore, ideally

Always create a secure random IV for every encryption of your Cipher

A new, random IV should be created for every encryption of data. Think of the IV as a nonce (number used once) - it's public but random and unpredictable. A secure random IV can be created as follows

cipher = ...
cipher.encrypt
key = cipher.random_key
iv = cipher.random_iv # also sets the generated IV on the Cipher

Although the key is generally a random value, too, it is a bad choice
as an IV. There are elaborate ways how an attacker can take advantage
of such an IV. As a general rule of thumb, exposing the key directly
or indirectly should be avoided at all cost and exceptions only be
made with good reason.

Calling Cipher#final

ECB (which should not be used) and CBC are both block-based modes. This means that unlike for the other streaming-based modes, they operate on fixed-size blocks of data, and therefore they require a “finalization” step to produce or correctly decrypt the last block of data by appropriately handling some form of padding. Therefore it is essential to add the output of OpenSSL::Cipher#final to your encryption/decryption buffer or you will end up with decryption errors or truncated data.

Although this is not really necessary for streaming-mode ciphers, it is still recommended to apply the same pattern of adding the output of Cipher#final there as well - it also enables you to switch between modes more easily in the future.

Encrypting and decrypting some data

data = "Very, very confidential data"

cipher = OpenSSL::Cipher::AES.new(128, :CBC)
cipher.encrypt
key = cipher.random_key
iv = cipher.random_iv

encrypted = cipher.update(data) + cipher.final
...
decipher = OpenSSL::Cipher::AES.new(128, :CBC)
decipher.decrypt
decipher.key = key
decipher.iv = iv

plain = decipher.update(encrypted) + decipher.final

puts data == plain #=> true

Authenticated Encryption and Associated Data (AEAD)

If the OpenSSL version used supports it, an Authenticated Encryption mode (such as GCM or CCM) should always be preferred over any unauthenticated mode. Currently, OpenSSL supports AE only in combination with Associated Data (AEAD) where additional associated data is included in the encryption process to compute a tag at the end of the encryption. This tag will also be used in the decryption process and by verifying its validity, the authenticity of a given ciphertext is established.

This is superior to unauthenticated modes in that it allows to detect if somebody effectively changed the ciphertext after it had been encrypted. This prevents malicious modifications of the ciphertext that could otherwise be exploited to modify ciphertexts in ways beneficial to potential attackers.

If no associated data is needed for encryption and later decryption, the OpenSSL library still requires a value to be set - “” may be used in case none is available. An example using the GCM (Galois Counter Mode):

cipher = OpenSSL::Cipher::AES.new(128, :GCM)
cipher.encrypt
key = cipher.random_key
iv = cipher.random_iv
cipher.auth_data = ""

encrypted = cipher.update(data) + cipher.final
tag = cipher.auth_tag

decipher = OpenSSL::Cipher::AES.new(128, :GCM)
decipher.decrypt
decipher.key = key
decipher.iv = iv
decipher.auth_tag = tag
decipher.auth_data = ""

plain = decipher.update(encrypted) + decipher.final

puts data == plain #=> true

Direct Known Subclasses

Cipher

Defined Under Namespace

Classes: Cipher, CipherError

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#new(string) ⇒ Object

The string must contain a valid cipher name like “AES-128-CBC” or “3DES”.

A list of cipher names is available by calling OpenSSL::Cipher.ciphers.



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# File 'ossl_cipher.c', line 111

static VALUE
ossl_cipher_initialize(VALUE self, VALUE str)
{
    EVP_CIPHER_CTX *ctx;
    const EVP_CIPHER *cipher;
    char *name;
    unsigned char key[EVP_MAX_KEY_LENGTH];

    name = StringValuePtr(str);
    GetCipherInit(self, ctx);
    if (ctx) {
	ossl_raise(rb_eRuntimeError, "Cipher already inititalized!");
    }
    AllocCipher(self, ctx);
    EVP_CIPHER_CTX_init(ctx);
    if (!(cipher = EVP_get_cipherbyname(name))) {
	ossl_raise(rb_eRuntimeError, "unsupported cipher algorithm (%s)", name);
    }
    /*
     * The EVP which has EVP_CIPH_RAND_KEY flag (such as DES3) allows
     * uninitialized key, but other EVPs (such as AES) does not allow it.
     * Calling EVP_CipherUpdate() without initializing key causes SEGV so we
     * set the data filled with "\0" as the key by default.
     */
    memset(key, 0, EVP_MAX_KEY_LENGTH);
    if (EVP_CipherInit_ex(ctx, cipher, NULL, key, NULL, -1) != 1)
	ossl_raise(eCipherError, NULL);

    return self;
}

Class Method Details

.OpenSSL::Cipher.ciphersObject

Returns the names of all available ciphers in an array.



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# File 'ossl_cipher.c', line 177

static VALUE
ossl_s_ciphers(VALUE self)
{
    VALUE ary;

    ary = rb_ary_new();
    OBJ_NAME_do_all_sorted(OBJ_NAME_TYPE_CIPHER_METH,
                    (void(*)(const OBJ_NAME*,void*))add_cipher_name_to_ary,
                    (void*)ary);

    return ary;
}

Instance Method Details

#auth_data=(string) ⇒ String

Sets the cipher's additional authenticated data. This field must be set when using AEAD cipher modes such as GCM or CCM. If no associated data shall be used, this method must still be called with a value of “”. The contents of this field should be non-sensitive data which will be added to the ciphertext to generate the authentication tag which validates the contents of the ciphertext.

The AAD must be set prior to encryption or decryption. In encryption mode, it must be set after calling Cipher#encrypt and setting Cipher#key= and Cipher#iv=. When decrypting, the authenticated data must be set after key, iv and especially after the authentication tag has been set. I.e. set it only after calling Cipher#decrypt, Cipher#key=, Cipher#iv= and Cipher#auth_tag= first.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 547

static VALUE
ossl_cipher_set_auth_data(VALUE self, VALUE data)
{
    EVP_CIPHER_CTX *ctx;
    unsigned char *in;
    long in_len, out_len;

    StringValue(data);

    in = (unsigned char *) RSTRING_PTR(data);
    in_len = RSTRING_LEN(data);

    GetCipher(self, ctx);

    if (!ossl_cipher_update_long(ctx, NULL, &out_len, in, in_len))
        ossl_raise(eCipherError, "couldn't set additional authenticated data");

    return data;
}

#auth_tag([ tag_len ]) ⇒ String

Gets the authentication tag generated by Authenticated Encryption Cipher modes (GCM for example). This tag may be stored along with the ciphertext, then set on the decryption cipher to authenticate the contents of the ciphertext against changes. If the optional integer parameter tag_len is given, the returned tag will be tag_len bytes long. If the parameter is omitted, the maximum length of 16 bytes will be returned. For maximum security, the default of 16 bytes should be chosen.

The tag may only be retrieved after calling Cipher#final.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 601

static VALUE
ossl_cipher_get_auth_tag(int argc, VALUE *argv, VALUE self)
{
    VALUE vtag_len;
    EVP_CIPHER_CTX *ctx;
    int nid, tag_len;

    if (rb_scan_args(argc, argv, "01", &vtag_len) == 0) {
	tag_len = 16;
    } else {
	tag_len = NUM2INT(vtag_len);
    }

    GetCipher(self, ctx);
    nid = EVP_CIPHER_CTX_nid(ctx);

    if (ossl_is_gcm(nid)) {
	return ossl_get_gcm_auth_tag(ctx, tag_len);
    } else {
	ossl_raise(eCipherError, "authentication tag not supported by this cipher");
	return Qnil; /* dummy */
    }
}

#auth_tag=(string) ⇒ String

Sets the authentication tag to verify the contents of the ciphertext. The tag must be set after calling Cipher#decrypt, Cipher#key= and Cipher#iv=, but before assigning the associated authenticated data using Cipher#auth_data= and of course, before decrypting any of the ciphertext. After all decryption is performed, the tag is verified automatically in the call to Cipher#final.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 644

static VALUE
ossl_cipher_set_auth_tag(VALUE self, VALUE vtag)
{
    EVP_CIPHER_CTX *ctx;
    int nid;
    unsigned char *tag;
    int tag_len;

    StringValue(vtag);
    tag = (unsigned char *) RSTRING_PTR(vtag);
    tag_len = RSTRING_LENINT(vtag);

    GetCipher(self, ctx);
    nid = EVP_CIPHER_CTX_nid(ctx);

    if (ossl_is_gcm(nid)) {
	ossl_set_gcm_auth_tag(ctx, tag, tag_len);
    } else {
	ossl_raise(eCipherError, "authentication tag not supported by this cipher");
    }

    return vtag;
}

#authenticated?Boolean

Indicated whether this Cipher instance uses an Authenticated Encryption mode.

Returns:

  • (Boolean)

Returns:

  • (Boolean)


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# File 'ossl_cipher.c', line 675

static VALUE
ossl_cipher_is_authenticated(VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    int nid;

    GetCipher(self, ctx);
    nid = EVP_CIPHER_CTX_nid(ctx);

    if (ossl_is_gcm(nid)) {
	return Qtrue;
    } else {
	return Qfalse;
    }
}

#block_sizeObject

#decryptself

Initializes the Cipher for decryption.

Make sure to call Cipher#encrypt or Cipher#decrypt before using any of the following methods:

  • key=, iv=, random_key, random_iv, pkcs5_keyivgen

Internally calls EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, 0).

Returns:

  • (self)


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# File 'ossl_cipher.c', line 288

static VALUE
ossl_cipher_decrypt(int argc, VALUE *argv, VALUE self)
{
    return ossl_cipher_init(argc, argv, self, 0);
}

#encryptself

Initializes the Cipher for encryption.

Make sure to call Cipher#encrypt or Cipher#decrypt before using any of the following methods:

  • key=, iv=, random_key, random_iv, pkcs5_keyivgen

Internally calls EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, 1).

Returns:

  • (self)


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# File 'ossl_cipher.c', line 270

static VALUE
ossl_cipher_encrypt(int argc, VALUE *argv, VALUE self)
{
    return ossl_cipher_init(argc, argv, self, 1);
}

#finalString

Returns the remaining data held in the cipher object. Further calls to Cipher#update or Cipher#final will return garbage. This call should always be made as the last call of an encryption or decryption operation, after after having fed the entire plaintext or ciphertext to the Cipher instance.

If an authenticated cipher was used, a CipherError is raised if the tag could not be authenticated successfully. Only call this method after setting the authentication tag and passing the entire contents of the ciphertext into the cipher.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 434

static VALUE
ossl_cipher_final(VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    int out_len;
    VALUE str;

    GetCipher(self, ctx);
    str = rb_str_new(0, EVP_CIPHER_CTX_block_size(ctx));
    if (!EVP_CipherFinal_ex(ctx, (unsigned char *)RSTRING_PTR(str), &out_len))
	ossl_raise(eCipherError, NULL);
    assert(out_len <= RSTRING_LEN(str));
    rb_str_set_len(str, out_len);

    return str;
}

#iv=(string) ⇒ String

Sets the cipher IV. Please note that since you should never be using ECB mode, an IV is always explicitly required and should be set prior to encryption. The IV itself can be safely transmitted in public, but it should be unpredictable to prevent certain kinds of attacks. You may use Cipher#random_iv to create a secure random IV.

Only call this method after calling Cipher#encrypt or Cipher#decrypt.

If not explicitly set, the OpenSSL default of an all-zeroes (“\0”) IV is used.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 511

static VALUE
ossl_cipher_set_iv(VALUE self, VALUE iv)
{
    EVP_CIPHER_CTX *ctx;

    StringValue(iv);
    GetCipher(self, ctx);

    if (RSTRING_LEN(iv) < EVP_CIPHER_CTX_iv_length(ctx))
        ossl_raise(eCipherError, "iv length too short");

    if (EVP_CipherInit_ex(ctx, NULL, NULL, NULL, (unsigned char *)RSTRING_PTR(iv), -1) != 1)
	ossl_raise(eCipherError, NULL);

    return iv;
}

#iv_lenObject

#key=(string) ⇒ String

Sets the cipher key. To generate a key, you should either use a secure random byte string or, if the key is to be derived from a password, you should rely on PBKDF2 functionality provided by OpenSSL::PKCS5. To generate a secure random-based key, Cipher#random_key may be used.

Only call this method after calling Cipher#encrypt or Cipher#decrypt.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 479

static VALUE
ossl_cipher_set_key(VALUE self, VALUE key)
{
    EVP_CIPHER_CTX *ctx;

    StringValue(key);
    GetCipher(self, ctx);

    if (RSTRING_LEN(key) < EVP_CIPHER_CTX_key_length(ctx))
        ossl_raise(eCipherError, "key length too short");

    if (EVP_CipherInit_ex(ctx, NULL, NULL, (unsigned char *)RSTRING_PTR(key), NULL, -1) != 1)
        ossl_raise(eCipherError, NULL);

    return key;
}

#key_lenObject

#key_len=(integer) ⇒ Integer

Sets the key length of the cipher. If the cipher is a fixed length cipher then attempting to set the key length to any value other than the fixed value is an error.

Under normal circumstances you do not need to call this method (and probably shouldn't).

See EVP_CIPHER_CTX_set_key_length for further information.

Returns:



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# File 'ossl_cipher.c', line 709

static VALUE
ossl_cipher_set_key_length(VALUE self, VALUE key_length)
{
    int len = NUM2INT(key_length);
    EVP_CIPHER_CTX *ctx;

    GetCipher(self, ctx);
    if (EVP_CIPHER_CTX_set_key_length(ctx, len) != 1)
        ossl_raise(eCipherError, NULL);

    return key_length;
}

#nameString

Returns the name of the cipher which may differ slightly from the original name provided.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 458

static VALUE
ossl_cipher_name(VALUE self)
{
    EVP_CIPHER_CTX *ctx;

    GetCipher(self, ctx);

    return rb_str_new2(EVP_CIPHER_name(EVP_CIPHER_CTX_cipher(ctx)));
}

#padding=(integer) ⇒ Integer

Enables or disables padding. By default encryption operations are padded using standard block padding and the padding is checked and removed when decrypting. If the pad parameter is zero then no padding is performed, the total amount of data encrypted or decrypted must then be a multiple of the block size or an error will occur.

See EVP_CIPHER_CTX_set_padding for further information.

Returns:



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# File 'ossl_cipher.c', line 733

static VALUE
ossl_cipher_set_padding(VALUE self, VALUE padding)
{
    EVP_CIPHER_CTX *ctx;
    int pad = NUM2INT(padding);

    GetCipher(self, ctx);
    if (EVP_CIPHER_CTX_set_padding(ctx, pad) != 1)
	ossl_raise(eCipherError, NULL);
    return padding;
}

#pkcs5_keyivgen(pass[, salt [, iterations [, digest]]]) ⇒ nil

Generates and sets the key/IV based on a password.

WARNING: This method is only PKCS5 v1.5 compliant when using RC2, RC4-40, or DES with MD5 or SHA1. Using anything else (like AES) will generate the key/iv using an OpenSSL specific method. This method is deprecated and should no longer be used. Use a PKCS5 v2 key generation method from OpenSSL::PKCS5 instead.

Parameters

salt must be an 8 byte string if provided. iterations is a integer with a default of 2048. digest is a Digest object that defaults to 'MD5'

A minimum of 1000 iterations is recommended.

Returns:

  • (nil)


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# File 'ossl_cipher.c', line 314

static VALUE
ossl_cipher_pkcs5_keyivgen(int argc, VALUE *argv, VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    const EVP_MD *digest;
    VALUE vpass, vsalt, viter, vdigest;
    unsigned char key[EVP_MAX_KEY_LENGTH], iv[EVP_MAX_IV_LENGTH], *salt = NULL;
    int iter;

    rb_scan_args(argc, argv, "13", &vpass, &vsalt, &viter, &vdigest);
    StringValue(vpass);
    if(!NIL_P(vsalt)){
	StringValue(vsalt);
	if(RSTRING_LEN(vsalt) != PKCS5_SALT_LEN)
	    ossl_raise(eCipherError, "salt must be an 8-octet string");
	salt = (unsigned char *)RSTRING_PTR(vsalt);
    }
    iter = NIL_P(viter) ? 2048 : NUM2INT(viter);
    digest = NIL_P(vdigest) ? EVP_md5() : GetDigestPtr(vdigest);
    GetCipher(self, ctx);
    EVP_BytesToKey(EVP_CIPHER_CTX_cipher(ctx), digest, salt,
		   (unsigned char *)RSTRING_PTR(vpass), RSTRING_LENINT(vpass), iter, key, iv);
    if (EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, -1) != 1)
	ossl_raise(eCipherError, NULL);
    OPENSSL_cleanse(key, sizeof key);
    OPENSSL_cleanse(iv, sizeof iv);

    return Qnil;
}

#random_ivObject

Generate, set, and return a random iv. You must call cipher.encrypt or cipher.decrypt before calling this method.



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# File 'lib/openssl/cipher.rb', line 48

def random_iv
  str = OpenSSL::Random.random_bytes(self.iv_len)
  self.iv = str
  return str
end

#random_keyObject

Generate, set, and return a random key. You must call cipher.encrypt or cipher.decrypt before calling this method.



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# File 'lib/openssl/cipher.rb', line 40

def random_key
  str = OpenSSL::Random.random_bytes(self.key_len)
  self.key = str
  return str
end

#resetself

Fully resets the internal state of the Cipher. By using this, the same Cipher instance may be used several times for encryption or decryption tasks.

Internally calls EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, -1).

Returns:

  • (self)


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# File 'ossl_cipher.c', line 202

static VALUE
ossl_cipher_reset(VALUE self)
{
    EVP_CIPHER_CTX *ctx;

    GetCipher(self, ctx);
    if (EVP_CipherInit_ex(ctx, NULL, NULL, NULL, NULL, -1) != 1)
	ossl_raise(eCipherError, NULL);

    return self;
}

#update(data[, buffer]) ⇒ String

Encrypts data in a streaming fashion. Hand consecutive blocks of data to the update method in order to encrypt it. Returns the encrypted data chunk. When done, the output of Cipher#final should be additionally added to the result.

Parameters

data is a nonempty string. buffer is an optional string to store the result.

Returns:

  • (String)


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# File 'ossl_cipher.c', line 384

static VALUE
ossl_cipher_update(int argc, VALUE *argv, VALUE self)
{
    EVP_CIPHER_CTX *ctx;
    unsigned char *in;
    long in_len, out_len;
    VALUE data, str;

    rb_scan_args(argc, argv, "11", &data, &str);

    StringValue(data);
    in = (unsigned char *)RSTRING_PTR(data);
    if ((in_len = RSTRING_LEN(data)) == 0)
        ossl_raise(rb_eArgError, "data must not be empty");
    GetCipher(self, ctx);
    out_len = in_len+EVP_CIPHER_CTX_block_size(ctx);
    if (out_len <= 0) {
	ossl_raise(rb_eRangeError,
		   "data too big to make output buffer: %ld bytes", in_len);
    }

    if (NIL_P(str)) {
        str = rb_str_new(0, out_len);
    } else {
        StringValue(str);
        rb_str_resize(str, out_len);
    }

    if (!ossl_cipher_update_long(ctx, (unsigned char *)RSTRING_PTR(str), &out_len, in, in_len))
	ossl_raise(eCipherError, NULL);
    assert(out_len < RSTRING_LEN(str));
    rb_str_set_len(str, out_len);

    return str;
}