Cross-platform cryptography

Elliptic key string signature conversion between DER and IEEE P1363 encoding

Please note that all following information is valid for the elliptic curve SECP256R1 that we are using in the programs. Using a curve with a longer size will give longer signatures.

There are two ECDSA signature formats "on the market" and here are the specifications:

1. IEEE P1363 = R|S = raw encoding: this encoding is easy to detect - the signature in byte form is exact 64 bytes long and a simple concatenation of the two values "R" and "S".

2. DER = ASN.1 encoding: this encoding contains some more bytes so it is around 70 bytes long (some bytes more or less are common). The two values "R" and "S" are embedded in a structure for better reading by some frameworks.

The conversion between the two formats sounds easy but when trying to do it on your own you will encounter a lot of hick ups. For that reason I'm providing converter from DER to IEEE P1363 and IEEE P1363 to DER - unfortunately only for a limited number of frameworks.

⚠️ Security warning ⚠️

This is a serious warning regarding the security of the programs shown in these article series. Always keep in mind my disclaimer regarding my programs: All programs are for educational purposes and are not intended to use in production or any other programs where a secure solution is needed. The programs do not have proper exceptional/error handling and in some cases they use insecure key lengths or other methods that are insecure. Never ever use the programs in real life unless checked by a qualified professional cryptographer.

The following links provide the solutions in code and an online compiler that runs the code.

Language	available	Online-compiler
Java DER to P1363	✅	repl.it CpcJavaEcSignatureConverterDerToP1363
Java P1363 to DER	✅	repl.it CpcJavaEcSignatureConverterP1363ToDer
PHP DER to P1363	✅	repl.it CpcPhpEcSignatureConverter
PHP P1363 to DER	✅	repl.it CpcPhpEcSignatureConverter
C#	❌	not available
Javascript CryptoJs	❌	not available
NodeJS Crypto DER to P1363	✅	repl.it CpcNodeJsCryptoEcSignatureConverterDerToP1363
NodeJS Crypto P1363 to DER	✅	repl.it CpcNodeJsCryptoEcSignatureConverterP1363ToDer
NodeJS forge	❌	not available
Webcrypto DER to P1363	✅	Your browser WebcryptoEcSignatureConverterDerToP1363.html
Webcrypto P1363 to DER	✅	Your browser WebcryptoEcSignatureConverterP1363ToDer.html
OpenSSL	❌	not available

Notes regarding the implementations: for this article I have choosen the DER encoding of the signature. Some frameworks support this kind of encoding "out of the box", e.g. in Java we choose the algorithm SHA256withECDSA and everything is fine. If you like need the example with IEEE P1363 encoding see this article.

The other important part is the key management. Some implementations will work with other curves, some implementations do have hard-coded import functions that will work with the named curve SECP256R1 only.

This is an output for DER to P1363 encoding:

EC signature converter DER to P1363 encoding
Please note that all values are in Base64 encoded form
signature in DER encoding:   MEUCIQCW98vDD+c/Wx3WX3T+Ph9ZDf1s5nuDThz2xrhSOjwGFAIgNpUg5SygNK7W+zzw4eNZkivizpU/UUXMMR2zPw2D7J4=
signature in P1363 encoding: lvfLww/nP1sd1l90/j4fWQ39bOZ7g04c9sa4Ujo8BhQ2lSDlLKA0rtb7PPDh41mSK+LOlT9RRcwxHbM/DYPsng==

This is an output for P1363 to DER encoding:

EC signature converter P1363 to DER encoding
Please note that all values are in Base64 encoded form
signature in P1363 encoding: aF1cTCPqSUuCSKMftzeE37VeaqrlQuILJsW9RBEo8yZUyZFTOkEqq2TI2Bd/kugow6bbZDfhtsB3QwbZ55aOmQ==
signature in DER encoding:   MEQCIGhdXEwj6klLgkijH7c3hN+1Xmqq5ULiCybFvUQRKPMmAiBUyZFTOkEqq2TI2Bd/kugow6bbZDfhtsB3QwbZ55aOmQ==

Last update: Jan. 08th 2021

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