SSH can also use RSA keys for authentication, only the SSH public key’s format is not If we want to extract the public key from the key pair, such as to send it out: $ openssl rsa -in key.pem -pubout -out public.pem $ openssl genpkey -out key.pem -algorithm rsa -pkeyopt rsa_keygen_bits:2048 -des3 Which allows various kind of public key algorithms to be used: $ openssl genpkey -out key.pem -algorithm rsa -pkeyopt rsa_keygen_bits:2048 Indeed, genrsa is deprecated and OpenSSL recommends to use genpkey instead, Public and private keys in ame file) can be generated by: $ openssl genrsa -out key.pem 1024Īnd optionally we can encrypt the keypair using a passphrase: $ openssl rsa -in key.pem -des3 -out enc-key.pem OpenSSL provides tools to generate key pairs. It in encryption, we must use it in decryption as well. $ openssl rsautl -decrypt -oaep -in -inkey private.pem -out small.txt If the input file is small enough, we can encrypt and decrypt using theįollowing commands: $ openssl rsautl -encrypt -oaep -in small.txt -pubin -inkey public.pem -out For example,Ģ048-bit RSA can only encrypt a file no more than 245 bytes Public key cryptography can only be used to encrypt a small file. To see if ECDSA can be used with message digest algorithms other than SHA1,Ĭheck $ openssl list-message-digest-algorithms $ openssl dgst -ecdsa-with-SHA1 -verify public.pem -signature signature.bin input.txt We can also use ellipticĬurve (ECDSA): $ openssl dgst -ecdsa-with-SHA1 -sign private.pem -out signature.bin input.txt The dgst version does not limit to RSA key pairs. The rsautl sign is signing without using the ASN1 encoding. Namely, the dgst sign is to create a hash in ASN1 encoding and signing theĪSN1 encoded hash. Indeed we can do both hashing and signing at the same time: $ openssl dgst -sha256 -sign private.pem -out signature.txt input.txtĪnd this can be verified with: $ openssl dgst -sha256 -verify public.pem -signature signature.txt input.txtīut the signature in this two approaches differ, Public.pem): $ openssl rsautl -verify -in signature.txt -out digest.txt -inkey public.pem -pubin The signature file will contain digest.txt and we can “verify” the signatureĪnd get back the digest.txt using the public key (assumed stored in Private key stored in private.pem: $ openssl rsautl -sign -in digest.txt -out signature.txt -inkey private.pem It, we use the RSA algorithm through the rsautl command in OpenSSL with a We can now have a small-size digest that correspond to the larger data. To see all supported we can use openssl list-message-digest-commands. The -sha256 is a hash algorithm, the alternatives are -sha1, -ripemd160, We should first generate a digest from a file usingĪ hash algorithm: $ openssl dgst -sha256 -out digest.txt input.txt This involves public key cryptography but we cannot use Digitally sign a fileĬryptography is not only for encryption. We usually use CBC, CFB, or OFB for better security. Operation: \(Y_i = E_K(IV+g(i))\) with IV=token() where \(g(i)\) is a deterministic function, usually an identity function.Plaintext blocks denoted by \(T_i,\ i=1,2,\cdots\) ciphertext blocks \(Z_i\) Įncryption function with key \(K\) denoted by \(E_K()\): Below are the summary of some common modes, with Mode of operaions is to address how we should handle multiple block of data inĮncryption using block cipher. The cbc stands for “cipherīlock chaining”, which is one of the many block cipher mode of Stream ciphers and others are block ciphers. OpenSSL supports a number ofĬiphers: AES, Blowfish, RC4, 3DES, RC2, DES, CAST5, SEED. The above example is using AES-256 as cipher. base64 that does not take password as base64 is just an encoding, not really To request for a salted password to be used. We can also provide an optional -salt flag to the enc command OpenSSL will ask for password from stdin if -pass is not provided in theĬommand line. $ openssl enc -aes-256-cbc -d -in -out plain.txt -pass pass:pa55w0rd To encrypt and decrypt a file, plain.txt, of arbitrary size, we use theįollowing commands respectively: $ openssl enc -aes-256-cbc -in plain.txt -out -pass pass:pa55w0rd Will look further into it in the following. The enc command can encrypt or decrypt a file, using symmetric ciphers. rsautl: to encrypt/decrypt or sign/verify signature with RSA.rand: generation of pseudo-random bit strings. genrsa: generate a pair of public/private key for RSA algorithm.to see all available ciphers: openssl list-cipher-commands.enc: encrypt/decrypt using symmetric key algorithms.We can see the list of all “commands” it supported by $ openssl list-standard-commands TheĪnswer is affirmative in OpenSSL but it is not straightforward. A natural question from using SSH for a while is whether weĬan reuse the SSH authentication key for other use, say, encrypting a file.
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