PureBasic

Understanding a few ECDSA Public Key Formats

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Describes a few ECDSA public key formats. PureBasic

IncludeFile "CkBinData.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkPublicKey.pb"

Procedure ChilkatExample()

    success.i = 0

    ; Here we have the output of the following openssl command:  openssl ec -in key.pem -pubout -text

    ; Private-Key: (256 bit)
    ; priv:
    ;     0e:63:25:8a:73:3c:71:b6:c0:e7:a3:0f:94:b9:74:
    ;     e0:be:bd:46:18:be:40:7e:66:9e:21:99:85:0e:ed:
    ;     87:2d
    ; pub:
    ;     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
    ;     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
    ;     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
    ;     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
    ;     12:b7:b8:6a:43
    ; ASN1 OID: prime256v1
    ; NIST CURVE: P-256
    ; writing EC key
    ; -----BEGIN PUBLIC KEY-----
    ; MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
    ; Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
    ; -----END PUBLIC KEY-----

    ; The public key is shown in two different formats.
    ; The first is this:

    ; pub:
    ;     04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:
    ;     b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:
    ;     39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:
    ;     2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:
    ;     12:b7:b8:6a:43

    ; It is the ANSI X9.63 format.
    ; 65-bytes are the uncompressed public key (04 || X || Y) 

    ; This is the same public key, but in PEM format

    ; -----BEGIN PUBLIC KEY-----
    ; MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
    ; Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
    ; -----END PUBLIC KEY-----

    ; It contains ASN.1 that more explicitly identifies the key type.
    ; 
    ; SEQUENCE (2 elem)
    ;   SEQUENCE (2 elem)
    ;     OBJECT IDENTIFIER 1.2.840.10045.2.1 ecPublicKey (ANSI X9.62 public key type)
    ;     OBJECT IDENTIFIER 1.2.840.10045.3.1.7 prime256v1 (ANSI X9.62 named elliptic curve)
    ;   BIT STRING (520 bit) 000001000101110100011010010011111101100110111101010010011001111011100...

    ; PEM format can be loaded into a Chilkat public key object like this:

    sbPem.i = CkStringBuilder::ckCreate()
    If sbPem.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringBuilder::ckAppend(sbPem,"-----BEGIN PUBLIC KEY-----" + Chr(13) + Chr(10))
    CkStringBuilder::ckAppend(sbPem,"MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET" + Chr(13) + Chr(10))
    CkStringBuilder::ckAppend(sbPem,"Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==" + Chr(13) + Chr(10))
    CkStringBuilder::ckAppend(sbPem,"-----END PUBLIC KEY-----" + Chr(13) + Chr(10))

    pubKey1.i = CkPublicKey::ckCreate()
    If pubKey1.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPublicKey::ckLoadFromString(pubKey1,CkStringBuilder::ckGetAsString(sbPem))
    If success = 0
        Debug CkPublicKey::ckLastErrorText(pubKey1)
        CkStringBuilder::ckDispose(sbPem)
        CkPublicKey::ckDispose(pubKey1)
        ProcedureReturn
    EndIf

    ; The X9.63 format can be loaded like this:
    sbHex.i = CkStringBuilder::ckCreate()
    If sbHex.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringBuilder::ckAppend(sbHex,"04:5d:1a:4f:d9:bd:49:9e:e4:fd:55:2c:0d:ea:6d:")
    CkStringBuilder::ckAppend(sbHex,"b1:66:64:7a:71:91:13:63:86:fe:ca:94:d4:47:51:")
    CkStringBuilder::ckAppend(sbHex,"39:66:ff:43:d5:62:de:f2:f2:41:3c:2e:3f:95:18:")
    CkStringBuilder::ckAppend(sbHex,"2d:23:f7:e7:8e:75:19:3b:c6:50:fb:d9:90:f5:e8:")
    CkStringBuilder::ckAppend(sbHex,"12:b7:b8:6a:43")

    ; Get rid of the ":" chars.
    numReplaced.i = CkStringBuilder::ckReplace(sbHex,":","")

    ; We'll need to convert hex to base64..
    bdKey.i = CkBinData::ckCreate()
    If bdKey.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkBinData::ckAppendEncoded(bdKey,CkStringBuilder::ckGetAsString(sbHex),"hex")

    pubKey2.i = CkPublicKey::ckCreate()
    If pubKey2.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPublicKey::ckLoadFromString(pubKey2,CkBinData::ckGetEncoded(bdKey,"base64"))
    If success = 0
        Debug CkPublicKey::ckLastErrorText(pubKey2)
        CkStringBuilder::ckDispose(sbPem)
        CkPublicKey::ckDispose(pubKey1)
        CkStringBuilder::ckDispose(sbHex)
        CkBinData::ckDispose(bdKey)
        CkPublicKey::ckDispose(pubKey2)
        ProcedureReturn
    EndIf

    ; Let's get the key in pubKey2 as PEM.
    ; It should be idential to the PEM above.
    Debug CkPublicKey::ckGetPem(pubKey2,1)

    ; Here's the output.  You can see it's the same as the PEM above..

    ; -----BEGIN PUBLIC KEY-----
    ; MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEXRpP2b1JnuT9VSwN6m2xZmR6cZET
    ; Y4b+ypTUR1E5Zv9D1WLe8vJBPC4/lRgtI/fnjnUZO8ZQ+9mQ9egSt7hqQw==
    ; -----END PUBLIC KEY-----


    CkStringBuilder::ckDispose(sbPem)
    CkPublicKey::ckDispose(pubKey1)
    CkStringBuilder::ckDispose(sbHex)
    CkBinData::ckDispose(bdKey)
    CkPublicKey::ckDispose(pubKey2)


    ProcedureReturn
EndProcedure