RSA(3)

User Contributed Perl Documentation

RSA(3)

NAME¶

Crypt::OpenSSL::RSA - RSA encoding and decoding, using the openSSL libraries

SYNOPSIS¶

  use Crypt::OpenSSL::Random;
  use Crypt::OpenSSL::RSA;
  # not necessary if we have /dev/random:
  Crypt::OpenSSL::Random::random_seed($good_entropy);
  Crypt::OpenSSL::RSA->import_random_seed();
  $rsa_pub = Crypt::OpenSSL::RSA->new_public_key($key_string);
  $ciphertext = $rsa->encrypt($plaintext);
  $rsa_priv = Crypt::OpenSSL::RSA->new_private_key($key_string);
  $plaintext = $rsa->decrypt($ciphertext);
  $rsa = Crypt::OpenSSL::RSA->generate_key(1024); # or
  $rsa = Crypt::OpenSSL::RSA->generate_key(1024, $prime);
  print "private key is:\n", $rsa->get_private_key_string();
  print "public key (in PKCS1 format) is:\n",
        $rsa->get_public_key_string();
  print "public key (in X509 format) is:\n",
        $rsa->get_public_key_x509_string();
  $rsa_priv->use_md5_hash(); # insecure. use_sha256_hash or use_sha1_hash are the default
  $signature = $rsa_priv->sign($plaintext);
  print "Signed correctly\n" if ($rsa->verify($plaintext, $signature));

SECURITY¶

Version 0.35 disabled PKCS#1 v1.5 padding entirely to mitigate the Marvin attack. However, the Marvin attack only affects PKCS#1 v1.5 decryption (padding oracle), not signatures. Version 0.38 re-enables use_pkcs1_padding() for use with sign() and verify(), while keeping it disabled for encrypt() and decrypt(). PKCS1_OAEP should be used for encryption and either PKCS1_PSS or PKCS1 can be used for signing.

DESCRIPTION¶

"Crypt::OpenSSL::RSA" provides the ability to RSA encrypt strings which are somewhat shorter than the block size of a key. It also allows for decryption, signatures and signature verification.

NOTE: Many of the methods in this package can croak, so use "eval", or Error.pm's try/catch mechanism to capture errors. Also, while some methods from earlier versions of this package return true on success, this (never documented) behavior is no longer the case.

Class Methods¶

new_public_key

Create a new "Crypt::OpenSSL::RSA" object by loading a public key in from a string containing either PEM or DER encoding of the PKCS#1 or X.509 representation of the key.

For PEM keys, the string should include the "-----BEGIN...-----" and "-----END...-----" lines. Both "BEGIN RSA PUBLIC KEY" (PKCS#1) and "BEGIN PUBLIC KEY" (X.509/SubjectPublicKeyInfo) formats are supported.

DER-encoded keys (raw binary ASN.1) are also accepted and the format (PKCS#1 vs X.509) is auto-detected.

The padding is set to PKCS1_OAEP, but can be changed with the "use_xxx_padding" methods.

Note, PKCS1_OAEP can only be used for encryption. Call "use_pkcs1_pss_padding" or "use_pkcs1_padding" prior to signing operations.

new_private_key

Create a new "Crypt::OpenSSL::RSA" object by loading a private key in from a string containing either PEM or DER encoding of the key.

For PEM keys, the string should include the "-----BEGIN...-----" and "-----END...-----" lines. The padding is set to PKCS1_OAEP, but can be changed with "use_xxx_padding".

DER-encoded keys (raw binary ASN.1) are also accepted.

An optional parameter can be passed for passphrase-protected private keys:

passphrase: The passphrase which protects the private key. For PEM keys, this decrypts traditional encrypted PEM ("DEK-Info" header) and encrypted PKCS#8 PEM ("BEGIN ENCRYPTED PRIVATE KEY"). For DER keys, this decrypts encrypted PKCS#8 DER ("EncryptedPrivateKeyInfo" ASN.1 structure).

generate_key

Create a new "Crypt::OpenSSL::RSA" object by constructing a private/public key pair. The first (mandatory) argument is the key size, while the second optional argument specifies the public exponent (the default public exponent is 65537). The padding is set to "PKCS1_OAEP", but can be changed with use_xxx_padding methods.

new_key_from_parameters

Given Crypt::OpenSSL::Bignum objects for n, e, and optionally d, p, and q, where p and q are the prime factors of n, e is the public exponent and d is the private exponent, create a new Crypt::OpenSSL::RSA object using these values. If p and q are provided and d is undef, d is computed. Note that while p and q are not necessary for a private key, their presence will speed up computation.

An optional "check => 1" parameter can be passed after the key components to validate the key immediately after construction:

  my $rsa = Crypt::OpenSSL::RSA->new_key_from_parameters(
      $n, $e, $d, $p, $q, check => 1
  );

When enabled, check_key() is called on the resulting key. If the key parameters are inconsistent (e.g. wrong CRT values, mismatched n/e/d/p/q), the constructor will croak instead of returning an object that fails at first use. The check is only performed on private keys; public-only keys (n and e only) are returned without validation.

import_random_seed

Import a random seed from Crypt::OpenSSL::Random, since the OpenSSL libraries won't allow sharing of random structures across perl XS modules.

Instance Methods¶

DESTROY

Clean up after ourselves. In particular, erase and free the memory occupied by the RSA key structure.

get_public_key_string

Return the Base64/DER-encoded PKCS1 representation of the public key. This string has header and footer lines:

  -----BEGIN RSA PUBLIC KEY------
  -----END RSA PUBLIC KEY------

get_public_key_pkcs1_string

Alias for "get_public_key_string". Returns the same PKCS#1 "RSAPublicKey" PEM format ("BEGIN RSA PUBLIC KEY"). Provided for naming symmetry with the import method "new_public_key" (which auto-detects PKCS#1 vs X.509) and with "get_public_key_x509_string".

get_public_key_x509_string

Return the Base64/DER-encoded representation of the "subject public key", suitable for use in X509 certificates. This string has header and footer lines:

  -----BEGIN PUBLIC KEY------
  -----END PUBLIC KEY------

and is the format that is produced by running "openssl rsa -pubout".

get_private_key_string

Return the Base64/DER-encoded PKCS1 representation of the private key. This string has header and footer lines:

  -----BEGIN RSA PRIVATE KEY------
  -----END RSA PRIVATE KEY------

2 optional parameters can be passed for passphrase protected private key string:

passphrase: The passphrase which protects the private key.
cipher name: The cipher algorithm used to protect the private key. Default to 'des3'.

get_private_key_pkcs8_string

Return the Base64/DER-encoded PKCS#8 representation of the private key. This string has header and footer lines:

  -----BEGIN PRIVATE KEY-----
  -----END PRIVATE KEY-----

This is the format produced by "openssl pkey -outform PEM", and is the private-key counterpart of "get_public_key_x509_string".

Accepts the same optional passphrase and cipher-name parameters as "get_private_key_string".

encrypt

Encrypt a binary "string" using the public (portion of the) key.

decrypt

Decrypt a binary "string". Croaks if the key is public only.

private_encrypt

Encrypt a binary "string" using the private key. Croaks if the key is public only. On OpenSSL 3.x, only "use_no_padding" and "use_pkcs1_padding" are supported; OAEP and PSS will croak.

public_decrypt

Decrypt a binary "string" using the public (portion of the) key. On OpenSSL 3.x, only "use_no_padding" and "use_pkcs1_padding" are supported; OAEP and PSS will croak.

sign

Sign a string using the secret (portion of the) key.

verify

Check the signature on a text.

Padding Methods¶

use_pkcs1_padding can be used for signature operations (sign() and verify()). PKCS#1 v1.5 encryption is disabled due to the Marvin attack. use_pkcs1_pss_padding is the recommended replacement for signatures. use_pkcs1_oaep_padding is used for encryption operations.

On OpenSSL 3.x, the appropriate padding is set for each operation unless use_no_padding or use_pkcs1_padding is called before the operation.

use_no_padding: Use raw RSA encryption. This mode should only be used to implement cryptographically sound padding modes in the application code. Encrypting user data directly with RSA is insecure.
use_pkcs1_padding: Use "PKCS #1 v1.5" padding for signature operations only. PKCS#1 v1.5 signatures (RSASSA-PKCS1-v1.5) are secure and widely required by protocols such as JWT RS256, ACME (RFC 8555), and SAML.
Note: PKCS#1 v1.5 encryption is disabled because it is vulnerable to the Marvin Attack <https://github.com/tomato42/marvin-toolkit/blob/master/README.md> (a timing side-channel on decryption padding validation). Calling encrypt() or decrypt() with this padding will croak. Use use_pkcs1_oaep_padding() for encryption.
use_pkcs1_oaep_padding: Use "EME-OAEP" padding as defined in PKCS #1 v2.0 with SHA-1, MGF1 and an empty encoding parameter. This mode of padding is recommended for all new applications. It is the default mode used by "Crypt::OpenSSL::RSA" but is only valid for encryption/decryption.
use_pkcs1_pss_padding: Use "RSA-PSS" padding as defined in PKCS#1 v2.1. In general, RSA-PSS should be used as a replacement for RSA-PKCS#1 v1.5. The module specifies the message digest being requested and the appropriate mgf1 setting and salt length for the digest.
Note: RSA-PSS cannot be used for encryption/decryption and results in a fatal error. Call "use_pkcs1_oaep_padding" for encryption operations.
use_sslv23_padding: Use "PKCS #1 v1.5" padding with an SSL-specific modification that denotes that the server is SSL3 capable.
Not available on OpenSSL 3.x or later. Calling this method will croak with a descriptive error message suggesting alternatives. Use use_pkcs1_oaep_padding() for encryption or use_pkcs1_pss_padding() for signatures.

Hash/Digest Methods¶

use_md5_hash: Use the RFC 1321 MD5 hashing algorithm by Ron Rivest when signing and verifying messages.
Note that this is considered insecure.
use_sha1_hash: Use the RFC 3174 Secure Hashing Algorithm (FIPS 180-1) when signing and verifying messages. This is the default, when use_sha256_hash is not available.
use_sha224_hash, use_sha256_hash, use_sha384_hash, use_sha512_hash: These FIPS 180-2 hash algorithms, for use when signing and verifying messages, are only available with newer openssl versions (>= 0.9.8).
use_sha256_hash is the default hash mode when available.
use_ripemd160_hash: Dobbertin, Bosselaers and Preneel's RIPEMD hashing algorithm when signing and verifying messages.
use_whirlpool_hash: Vincent Rijmen und Paulo S. L. M. Barreto ISO/IEC 10118-3:2004 WHIRLPOOL hashing algorithm when signing and verifying messages.
size: Returns the size, in bytes, of the key. All encrypted text will be of this size, and depending on the padding mode used, the length of the text to be encrypted should be:

pkcs1_oaep_padding: at most 42 bytes less than this size.
pkcs1_padding or sslv23_padding: at most 11 bytes less than this size.
no_padding: exactly this size.

check_key: This function validates the RSA key, returning a true value if the key is valid, and a false value otherwise. Croaks if the key is public only.
get_key_parameters: Return "Crypt::OpenSSL::Bignum" objects representing the values of "n", "e", "d", "p", "q", "d mod (p-1)", "d mod (q-1)", and "1/q mod p", where "p" and "q" are the prime factors of "n", "e" is the public exponent and "d" is the private exponent. Some of these values may return as "undef"; only "n" and "e" will be defined for a public key. The "Crypt::OpenSSL::Bignum" module must be installed for this to work.
is_private: Return true if this is a private key, and false if it is public only.

AUTHOR¶

Ian Robertson, "iroberts@cpan.org". For support, please email "perl-openssl-users@lists.sourceforge.net".