File.md

Class: Defuse\Crypto\File

Instance Methods

This class has no instance methods.

Static Methods

File::encryptFile($inputFilename, $outputFilename, Key $key)

Description:

Encrypts a file using a secret key.

Parameters:

1. $inputFilename is the path to a file containing the plaintext to encrypt.
2. $outputFilename is the path to save the ciphertext file.
3. $key is an instance of Key containing the secret key for encryption.

Behavior:

Encrypts the contents of the input file, writing the result to the output file. If the output file already exists, it is overwritten.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

Side-effects and performance:

None.

Cautions:

The ciphertext output by this method is decryptable by anyone with knowledge of the key $key. It is the caller's responsibility to keep $key secret. Where $key should be stored is up to the caller and depends on the threat model the caller is designing their application under. If you are unsure where to store $key, consult with a professional cryptographer to get help designing your application.

Please note that encryption does not, and is not intended to, hide the length of the data being encrypted. For example, it is not safe to encrypt a field in which only a small number of different-length values are possible (e.g. "male" or "female") since it would be possible to tell what the plaintext is by looking at the length of the ciphertext. In order to do this safely, it is your responsibility to, before encrypting, pad the data out to the length of the longest string that will ever be encrypted. This way, all plaintexts are the same length, and no information about the plaintext can be gleaned from the length of the ciphertext.

File::decryptFile($inputFilename, $outputFilename, Key $key)

Description:

Decrypts a file using a secret key.

Parameters:

1. $inputFilename is the path to a file containing the ciphertext to decrypt.
2. $outputFilename is the path to save the decrypted plaintext file.
3. $key is an instance of Key containing the secret key for decryption.

Behavior:

Decrypts the contents of the input file, writing the result to the output file. If the output file already exists, it is overwritten.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

• Defuse\Crypto\Exception\WrongKeyOrModifiedCiphertextException is thrown if the $key is not the correct key for the given ciphertext, or if the ciphertext has been modified (possibly maliciously). There is no way to distinguish between these two cases.

Side-effects and performance:

The input ciphertext is processed in two passes. The first pass verifies the integrity and the second pass performs the actual decryption of the file and writing to the output file. This is done in a streaming manner so that only a small part of the file is ever loaded into memory at a time.

Cautions:

Be aware that when Defuse\Crypto\WrongKeyOrModifiedCiphertextException is thrown, some partial plaintext data may have been written to the output. Any plaintext data that is output is guaranteed to be a prefix of the original plaintext (i.e. at worst it was truncated). This can only happen if an attacker modifies the input between the first pass (integrity check) and the second pass (decryption) over the file.

It is impossible in principle to distinguish between the case where you attempt to decrypt with the wrong key and the case where you attempt to decrypt a modified (corrupted) ciphertext. It is up to the caller how to best deal with this ambiguity, as it depends on the application this library is being used in. If in doubt, consult with a professional cryptographer.

File::encryptFileWithPassword($inputFilename, $outputFilename, $password)

Description:

Encrypts a file with a password.

Parameters:

1. $inputFilename is the path to a file containing the plaintext to encrypt.
2. $outputFilename is the path to save the ciphertext file.
3. $password is the password used for decryption.

Behavior:

Encrypts the contents of the input file, writing the result to the output file. If the output file already exists, it is overwritten.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

Side-effects and performance:

This method is intentionally slow, using a lot of CPU resources for a fraction of a second. It applies key stretching to the password in order to make password guessing attacks more computationally expensive. If you need a faster way to encrypt multiple ciphertexts under the same password, see the KeyProtectedByPassword class.

Cautions:

PHP stack traces display (portions of) the arguments passed to methods on the call stack. If an exception is thrown inside this call, and it is uncaught, the value of $password may be leaked out to an attacker through the stack trace. We recommend configuring PHP to never output stack traces (either displaying them to the user or saving them to log files).

Please note that encryption does not, and is not intended to, hide the length of the data being encrypted. For example, it is not safe to encrypt a field in which only a small number of different-length values are possible (e.g. "male" or "female") since it would be possible to tell what the plaintext is by looking at the length of the ciphertext. In order to do this safely, it is your responsibility to, before encrypting, pad the data out to the length of the longest string that will ever be encrypted. This way, all plaintexts are the same length, and no information about the plaintext can be gleaned from the length of the ciphertext.

File::decryptFileWithPassword($inputFilename, $outputFilename, $password)

Description:

Decrypts a file with a password.

Parameters:

1. $inputFilename is the path to a file containing the ciphertext to decrypt.
2. $outputFilename is the path to save the decrypted plaintext file.
3. $password is the password used for decryption.

Behavior:

Decrypts the contents of the input file, writing the result to the output file. If the output file already exists, it is overwritten.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

• Defuse\Crypto\Exception\WrongKeyOrModifiedCiphertextException is thrown if the $password is not the correct key for the given ciphertext, or if the ciphertext has been modified (possibly maliciously). There is no way to distinguish between these two cases.

Side-effects and performance:

This method is intentionally slow, using a lot of CPU resources for a fraction of a second. It applies key stretching to the password in order to make password guessing attacks more computationally expensive. If you need a faster way to encrypt multiple ciphertexts under the same password, see the KeyProtectedByPassword class.

The input ciphertext is processed in two passes. The first pass verifies the integrity and the second pass performs the actual decryption of the file and writing to the output file. This is done in a streaming manner so that only a small part of the file is ever loaded into memory at a time.

Cautions:

PHP stack traces display (portions of) the arguments passed to methods on the call stack. If an exception is thrown inside this call, and it is uncaught, the value of $password may be leaked out to an attacker through the stack trace. We recommend configuring PHP to never output stack traces (either displaying them to the user or saving them to log files).

Be aware that when Defuse\Crypto\WrongKeyOrModifiedCiphertextException is thrown, some partial plaintext data may have been written to the output. Any plaintext data that is output is guaranteed to be a prefix of the original plaintext (i.e. at worst it was truncated). This can only happen if an attacker modifies the input between the first pass (integrity check) and the second pass (decryption) over the file.

It is impossible in principle to distinguish between the case where you attempt to decrypt with the wrong password and the case where you attempt to decrypt a modified (corrupted) ciphertext. It is up to the caller how to best deal with this ambiguity, as it depends on the application this library is being used in. If in doubt, consult with a professional cryptographer.

File::encryptResource($inputHandle, $outputHandle, Key $key)

Description:

Encrypts a resource (stream) with a secret key.

Parameters:

1. $inputHandle is a handle to a resource (like a file pointer) containing the plaintext to encrypt.
2. $outputHandle is a handle to a resource (like a file pointer) that the ciphertext will be written to.
3. $key is an instance of Key containing the secret key for encryption.

Behavior:

Encrypts the data read from the input stream and writes it to the output stream.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

Side-effects and performance:

None.

Cautions:

The ciphertext output by this method is decryptable by anyone with knowledge of the key $key. It is the caller's responsibility to keep $key secret. Where $key should be stored is up to the caller and depends on the threat model the caller is designing their application under. If you are unsure where to store $key, consult with a professional cryptographer to get help designing your application.

Please note that encryption does not, and is not intended to, hide the length of the data being encrypted. For example, it is not safe to encrypt a field in which only a small number of different-length values are possible (e.g. "male" or "female") since it would be possible to tell what the plaintext is by looking at the length of the ciphertext. In order to do this safely, it is your responsibility to, before encrypting, pad the data out to the length of the longest string that will ever be encrypted. This way, all plaintexts are the same length, and no information about the plaintext can be gleaned from the length of the ciphertext.

File::decryptResource($inputHandle, $outputHandle, Key $key)

Description:

Decrypts a resource (stream) with a secret key.

Parameters:

1. $inputHandle is a handle to a file-backed resource containing the ciphertext to decrypt. It must be a file not a network stream or standard input.
2. $outputHandle is a handle to a resource (like a file pointer) that the plaintext will be written to.
3. $key is an instance of Key containing the secret key for decryption.

Behavior:

Decrypts the data read from the input stream and writes it to the output stream.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

• Defuse\Crypto\Exception\WrongKeyOrModifiedCiphertextException is thrown if the $key is not the correct key for the given ciphertext, or if the ciphertext has been modified (possibly maliciously). There is no way to distinguish between these two cases.

Side-effects and performance:

The input ciphertext is processed in two passes. The first pass verifies the integrity and the second pass performs the actual decryption of the file and writing to the output file. This is done in a streaming manner so that only a small part of the file is ever loaded into memory at a time.

Cautions:

Be aware that when Defuse\Crypto\WrongKeyOrModifiedCiphertextException is thrown, some partial plaintext data may have been written to the output. Any plaintext data that is output is guaranteed to be a prefix of the original plaintext (i.e. at worst it was truncated). This can only happen if an attacker modifies the input between the first pass (integrity check) and the second pass (decryption) over the file.

It is impossible in principle to distinguish between the case where you attempt to decrypt with the wrong key and the case where you attempt to decrypt a modified (corrupted) ciphertext. It is up to the caller how to best deal with this ambiguity, as it depends on the application this library is being used in. If in doubt, consult with a professional cryptographer.

File::encryptResourceWithPassword($inputHandle, $outputHandle, $password)

Description:

Encrypts a resource (stream) with a password.

Parameters:

1. $inputHandle is a handle to a resource (like a file pointer) containing the plaintext to encrypt.
2. $outputHandle is a handle to a resource (like a file pointer) that the ciphertext will be written to.
3. $password is the password used for encryption.

Behavior:

Encrypts the data read from the input stream and writes it to the output stream.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

Side-effects and performance:

This method is intentionally slow, using a lot of CPU resources for a fraction of a second. It applies key stretching to the password in order to make password guessing attacks more computationally expensive. If you need a faster way to encrypt multiple ciphertexts under the same password, see the KeyProtectedByPassword class.

Cautions:

PHP stack traces display (portions of) the arguments passed to methods on the call stack. If an exception is thrown inside this call, and it is uncaught, the value of $password may be leaked out to an attacker through the stack trace. We recommend configuring PHP to never output stack traces (either displaying them to the user or saving them to log files).

Please note that encryption does not, and is not intended to, hide the length of the data being encrypted. For example, it is not safe to encrypt a field in which only a small number of different-length values are possible (e.g. "male" or "female") since it would be possible to tell what the plaintext is by looking at the length of the ciphertext. In order to do this safely, it is your responsibility to, before encrypting, pad the data out to the length of the longest string that will ever be encrypted. This way, all plaintexts are the same length, and no information about the plaintext can be gleaned from the length of the ciphertext.

File::decryptResourceWithPassword($inputHandle, $outputHandle, $password)

Description:

Decrypts a resource (stream) with a password.

Parameters:

1. $inputHandle is a handle to a file-backed resource containing the ciphertext to decrypt. It must be a file not a network stream or standard input.
2. $outputHandle is a handle to a resource (like a file pointer) that the plaintext will be written to.
3. $password is the password used for decryption.

Behavior:

Decrypts the data read from the input stream and writes it to the output stream.

Return value:

Does not return a value.

Exceptions:

• Defuse\Crypto\Exception\IOException is thrown if there is an I/O error.

• Defuse\Crypto\Exception\EnvironmentIsBrokenException is thrown either when the platform the code is running on cannot safely perform encryption for some reason (e.g. it lacks a secure random number generator), or the runtime tests detected a bug in this library.

• Defuse\Crypto\Exception\WrongKeyOrModifiedCiphertextException is thrown if the $password is not the correct key for the given ciphertext, or if the ciphertext has been modified (possibly maliciously). There is no way to distinguish between these two cases.

Side-effects and performance:

This method is intentionally slow, using a lot of CPU resources for a fraction of a second. It applies key stretching to the password in order to make password guessing attacks more computationally expensive. If you need a faster way to encrypt multiple ciphertexts under the same password, see the KeyProtectedByPassword class.

The input ciphertext is processed in two passes. The first pass verifies the integrity and the second pass performs the actual decryption of the file and writing to the output file. This is done in a streaming manner so that only a small part of the file is ever loaded into memory at a time.

Cautions:

PHP stack traces display (portions of) the arguments passed to methods on the call stack. If an exception is thrown inside this call, and it is uncaught, the value of $password may be leaked out to an attacker through the stack trace. We recommend configuring PHP to never output stack traces (either displaying them to the user or saving them to log files).

Be aware that when Defuse\Crypto\WrongKeyOrModifiedCiphertextException is thrown, some partial plaintext data may have been written to the output. Any plaintext data that is output is guaranteed to be a prefix of the original plaintext (i.e. at worst it was truncated). This can only happen if an attacker modifies the input between the first pass (integrity check) and the second pass (decryption) over the file.

It is impossible in principle to distinguish between the case where you attempt to decrypt with the wrong password and the case where you attempt to decrypt a modified (corrupted) ciphertext. It is up to the caller how to best deal with this ambiguity, as it depends on the application this library is being used in. If in doubt, consult with a professional cryptographer.