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    Cryptography Why does EcdsaKoblitzSignature2016 use a "magic header"?

    January 30, 2018

    Cryptography Why does EcdsaKoblitzSignature2016 use a "magic header"?

    Why does EcdsaKoblitzSignature2016 use a "magic header"?

    Posted: 29 Jan 2018 07:34 PM PST

    EcdsaKoblitzSignature2016 is a digital signature algorithm of JSON-LD messages, implemented here. It is originally used by the Electrum wallet software. As per here, here and here, instead of using sign(...) directly, the algorithm adds a weird magic header before the message; then, the magic header plus the message is SHA-256 hashed. (it will be internally hashed again in the sign function)

    padded = "\x18Bitcoin Signed Message:\n" + num_to_var_int(len(message)) + message return sha256(padded)

    Even libsecp256k1 does not add this magic header. Is there a the point behind this magic header, or just a bad habit and a "shitty" use of ECC?

    submitted by /u/TK4U65BTQ6RQ
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    trying to understand the elliptic curve format for XML Signatures

    Posted: 29 Jan 2018 12:24 PM PST

    https://www.w3.org/TR/xmldsig-core/#sec-ECKeyValue gives the following example of an ECDSA key:

    <ECKeyValue xmlns="http://www.w3.org/2009/xmldsig11#"> <NamedCurve URI="urn:oid:1.2.840.10045.3.1.7" /> <PublicKey> vWccUP6Jp3pcaMCGIcAh3YOev4gaa2ukOANC7Ufg Cf8KDO7AtTOsGJK7/TA8IC3vZoCy9I5oPjRhyTBulBnj7Y </PublicKey> </ECKeyValue>

    Here's what it says regarding the encoding of the PublicKey:

    The PublicKey element contains a Base64 encoding of a binary representation of the x and y coordinates of the point. Its value is computed as follows:

    • Convert the elliptic curve point (x,y) to an octet string by first converting the field elements x and y to octet strings as specified in Section 6.2 of [ECC-ALGS] (note), and then prepend the concatenated result of the conversion with 0x04. Support for Elliptic-Curve-Point-to-Octet-String conversion without point compression is required.
    • Base64 encode the octet string resulting from the conversion in Step 1.

    From that I'd expect that the first character of the base64 decoded text would be 04 but it isn't. It's BD. Here's the full decoded value:

    bd671c50fe89a77a5c68c08621c021dd839ebf881a6b6ba4380342ed47e009ff0a0ceec0b533ac1892bbfd303c202def6680b2f48e683e3461c9306e9419e3ed

    So what gives? Am I misunderstanding something or is the example they provide a bad one? If the latter then where might I find a good example?

    submitted by /u/neubert2
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    Where can I find free creditable research papers for my senior seminar project for my research?

    Posted: 29 Jan 2018 07:34 AM PST

    I looked around a few places but not much content or it's pay-walled.

    Thank you in advance.

    submitted by /u/subless
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    Cryptography as Service

    Posted: 29 Jan 2018 07:07 PM PST

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    submitted by /u/anish2good
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    Question about prime numbers and cryptography

    Posted: 29 Jan 2018 04:33 AM PST

    What happens when a large number supposed to be prime is chosen via an algorithm that has flaws (such as Fermat pseudo prime numbers) and the number is not prime?

    For instance on a diffie-helman handshake?

    submitted by /u/3rssi
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